PC World 1999 August/PCWorld_1999-08_cd.bin/doc/HOWTO/PPP-HOWTO

Text File | 1997-04-15 | 159KB | 3,714 lines

  Linux PPP HOWTO
  Robert Hart, [e-mail]
  v3.0, 31 March 1997

  This document shows how to connect your Linux PC to a PPP server, how
  to use PPP to link two LANs together and provides one method of set¡
  ting up your Linux computer as a PPP server.The document also provides
  help in debugging non-functional PPP connections.

  Copyright

  This document is distributed under the terms of the GPL (GNU Public
  License).

  Distribution

  This document will be posted to comp.os.linux.answers as new versions
  of the document are produced. It is also available in HTML format at:-

  ╖  Linux Howto Index <http://sunsite.unc.edu/mdw/linux.html#howto>

  ╖  PPP-HOWTO <http://www.interweft.com.au/other/ppp-howto/ppp-
     howto.html>

  Other formats (SGML, ASCII, postscript, DVI) are available from Howtos
  - other formats <ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/other-
  formats>.

  As sunsite.unc.edu carries a very heavy load, please use an
  appropriate mirror site close to you.

  Acknowledgements

  A growing number of people have provided me with assistance in
  preparing this document. Special thanks go to Al Longyear for the
  guidance on PPP itself (if there are mistakes here, they are mine not
  his), Greg Hankins (maintainer of the Linux Howto system)and Debi
  Tackett (of MaximumAccess.com) for many helpful suggestions on style,
  content order, logic and clarity of explanations.

  Finally, to the many people who have contacted me by email offering
  comments - my thanks. As with all HOWTO authors,  the satisfaction of
  helping is all the payment we receive and it is enough. By writing
  this HOWTO I am repaying in a small way the debt I - and all other
  Linux users - owe to the people who write and maintain our OS of
  choice.

  1.  Introduction

  PPP (the Point to Point Protocol) is a mechanism for creating and
  running IP  (the Internet Protocol) and other network protocols over a
  serial link - be that a direct serial connection (using a null-modem
  cable), over a telnet established link or a link made using modems and
  telephone lines (and of course using digital lines such as ISDN).

  Using PPP, you can connect your Linux PC to a PPP server and access
  the resources of the network to which the server is connected (almost)
  as if you were directly connected to that network.

  You can also set up your Linux PC as a PPP server, so that other
  computers can dial into your computer and access the resources on your
  local PC and/or network.

  As PPP is a peer-to-peer system, you can also use PPP on two Linux PCs
  to link together two networks (or a local network to the Internet),
  creating a Wide Area Network (WAN).

  One major difference between PPP and an Ethernet connection is of
  course speed - a standard Ethernet connection operates at 10 Mbs (Mega
  - million bits per second) maximum theoretical throughput, whereas an
  analogue modem operates at speeds up to 56 kbps (kilo - thousand bits
  per second).

  Also, depending on the type of PPP connection, there may be some
  limitations in usage of some applications and services.

  1.1.  Clients and Servers

  PPP is strictly a peer to peer protocol; there is (technically) no
  difference between the machine that dials in and the machine that is
  dialed into. However, for clarity's sake, it is useful to think in
  terms of servers and clients.

  When you dial into a site to establish a PPP connection, you are a
  client. The machine to which you connect is the server.

  When you are setting up a Linux box to receive and handle dial in PPP
  connections, you are setting up a PPP server.

  Any Linux PC can be both a PPP server and client - even simultaneously
  if you have more than one serial port (and modem if necessary). As
  stated above, there is no real difference between clients and servers
  as far as PPP is concerned, once the connection is made.

  This document refers to the machine that initiates the call (that
  dials in) as the CLIENT, whilst the machine that answers the
  telephone, checks the authentication of the dial in request (using
  user names, passwords and possibly other mechanisms) is referred to as
  the SERVER.

  The use of PPP as a client to link one or more machines at a location
  into the Internet is, probably, the one in which  most people are
  interested - that is using their Linux PC as a client.

  The procedure described in this document will allow you to establish
  and automate your Internet connection.

  This document will also give you guidance in setting up your Linux PC
  as a PPP server and in linking two LANs together (with full routing)
  using PPP (this is frequently characterised as establishing a WAN -
  wide area network - link).

  1.2.  Differences between Linux distributions

  There are many different Linux distributions and they all have their
  own idiosyncrasies and ways of doing things.

  In particular, there are two different ways a Linux (and Unix)
  computer actually starts up, configures its interfaces and so forth.

  These are BSD system initialisation and System V system
  initialisation. If you dip into some of the Unix news groups, you will
  find occasional religious wars between proponents of these two
  systems. If that sort of thing amuses you, have fun burning bandwidth
  and join in!

  Possibly the most widely used distributions are

  ╖  Slackware
     which uses BSD style system initialisation

  ╖  Red Hat (and its former associate Caldera)
     which use SysV system initialisation (although in a slightly
     modified form)

  ╖  Debian
     which uses SysV system initialisation

  BSD style initialisation typically keeps its initialisation files in
  /etc/... and these files are:-

  ______________________________________________________________________
          /etc/rc
          /etc/rc.local
          /etc/rc.serial
                  (and possibly other files)
  ______________________________________________________________________

  Of recent times, some BSD system initialisation schemes use a
  /etc/rc.d...  directory to hold the start up file rather than putting
  everything into /etc.

  System V initialisation keeps its initialisation files in directories
  under /etc/... or  /etc/rc.d/... and a number of subdirectories under
  there:-

  ______________________________________________________________________
  drwxr-xr-x   2 root     root         1024 Jul  6 15:12 init.d
  -rwxr-xr-x   1 root     root         1776 Feb  9 05:01 rc
  -rwxr-xr-x   1 root     root          820 Jan  2  1996 rc.local
  -rwxr-xr-x   1 root     root         2567 Jul  5 20:30 rc.sysinit
  drwxr-xr-x   2 root     root         1024 Jul  6 15:12 rc0.d
  drwxr-xr-x   2 root     root         1024 Jul  6 15:12 rc1.d
  drwxr-xr-x   2 root     root         1024 Jul  6 15:12 rc2.d
  drwxr-xr-x   2 root     root         1024 Jul 18 18:07 rc3.d
  drwxr-xr-x   2 root     root         1024 May 27  1995 rc4.d
  drwxr-xr-x   2 root     root         1024 Jul  6 15:12 rc5.d
  drwxr-xr-x   2 root     root         1024 Jul  6 15:12 rc6.d
  ______________________________________________________________________

  If you are trying to track down where your Ethernet interface and
  associated network routes are actually configured, you will need to
  track through these files to actually find where the commands are that
  do this.

  1.3.  Distribution specific PPP configuration tools

  On some installations (for example Red Hat and Caldera), there is a X
  Windows configured PPP dial up system. This HOWTO does not cover these
  distribution specific tools. If you are having problems with them,
  contact the distributors directly!

  For Red Hat 4.x users, there is now a Red Hat PPP-TIP
  <http://www.interweft.com.au> in the Linux resources area and also
  from Red Hat Software <http://www.redhat.com> in the support area.

  2.  IP Numbers

  Every device that connects to the Internet must have its own, unique
  IP number. These are assigned centrally by a designated authority for
  each country.

  If you are connecting a local area network (LAN) to the Internet, YOU
  MUST use an IP number from your own assigned network range for all the
  computers and devices you have on your LAN. You MUST NOT pick IP
  numbers out of the air and use these whilst connecting to another LAN
  (let alone the Internet). At worst this will simply not work at all
  and could cause total havoc as your 'stolen' IP number starts
  interfering with the communications of another computer that is
  already using the IP number you have picked out of the air.

  Please note that the IP numbers used throughout this document (with
  some exceptions) are from the 'unconnected network numbers' series
  that are reserved for use by networks that are not (ever) connected to
  the Internet.

  There are IP numbers that are specifically dedicated to LANs that do
  not connect to the Internet. The IP number sequences are:-

  ╖  One A Class Network Address
     10.0.0.0 (netmask 255.0.0.0)
  ╖  16 B Class Network Addresses
     172.16.0.0 - 172.31.0.0 (netmask 255.255.0.0)

  ╖  256 C Class Network Addresses
     192.168.0.0 - 192.168.255.0 (netmask 255.255.255.0)

  If you have a LAN for which you have not been allocated IP numbers by
  the responsible authority in your country, you should use one of the
  network numbers from the above sequences for your machines.

  These numbers should never be used on the Internet.

  However, they can be used for the local Ethernet on a machine that is
  connecting to the Internet. This is because IP numbers are actually
  allocated to a network interface, not to a computer. So whilst your
  Ethernet interface may use 10.0.0.1 (for example), when you hook onto
  the Internet using PPP, your PPP interface will be given another (and
  valid) IP number by the server. Your PC will have Internet
  connectivity, but the other computers on your LAN will not.

  However, using Linux and the IP Masquerade (also known as NAT -
  Network address Translation) capabilities of the Linux and the ipfwadm
  software, you can connect your LAN to the Internet (with some
  restriction of services), even if you do not have valid IP numbers for
  the machines on your Ethernet.

  For more information on how to do this see the IP Masquerade mini-
  HOWTO at Linux IP Masquerade mini HOWTO
  <http://sunsite.unc.edu/mdw/HOWTO/mini/IP-Masquerade>

  For most users, who are connecting a single machine to an Internet
  service provider via PPP, obtaining an IP number (or more accurately,
  a network number) will not be necessary.

  If you wish to connect a small LAN to the Internet, many Internet
  Service Providers (ISPs) can provide you with a dedicated subnet (a
  specific sequence of IP numbers) from their existing IP address space.
  Alternatively, use IP Masquerading.

  For users, who are connecting a single PC to the Internet via an ISP,
  most providers use dynamic IP number assignment. That is, as part of
  the connection process, the PPP service you contact will tell your
  machine what IP number to use for the PPP interface during the current
  session. This number will not be the same every time you connect to
  your ISP.

  With dynamic IP numbers, you are not given the same IP number each
  time you connect. This has implications for server type applications
  on your Linux machine such as sendmail, ftpd, httpd and so forth.
  These services are based on the premise that the computer offering the
  service is accessible at the same IP number all the time (or at least
  the same fully qualified domain name - FQDN - and that DNS resolution
  of the name to IP address is available).

  The limitations of service due to dynamic IP number assignment (and
  ways to work around these, where possible) are discussed later in the
  document.

  3.  Aims of this Document

  3.1.  Setting up a PPP Client

  This document provides guidance to people who wish to use Linux and
  PPP to dial into a PPP server and set up an IP connection using PPP.
  It assumes that PPP has been compiled and installed on your Linux
  machine (but does briefly cover reconfiguring/recompiling your kernel
  to include PPP support).

  Whilst DIP (the standard way of creating a SLIP connection) can be
  used to set up a PPP connection, DIP scripts are generally quite
  complex. For this reason, this document does NOT cover using DIP to
  set up a PPP connection.

  Instead, this document describes the standard Linux PPP software
  (chat/pppd).

  3.2.  Linking two LANs or a LAN to the Internet using PPP

  This document provides (basic) information on linking two LANs or a
  LAN to the Internet using PPP.

  3.3.  Setting up a PPP server

  This document provides guidance on how to configure your Linux PC as a
  PPP server (allowing other people to dial into your Linux PC and
  establish a PPP connection).

  You should note that there are a myriad of ways of setting up Linux as
  a PPP server. This document gives one method - that used by the author
  to set up several small PPP servers (each of 16 modems).

  This method is known to work well. However, it is not necessarily the
  best method.

  3.4.  Using PPP over a direct null modem connection

  This document provides a brief overview of using PPP to link two Linux
  PCs via a null modem cable. It is possible to link other OS's to Linux
  this way as well. To do so, you will need to consult the documentation
  for the operating system you are interested in.

  3.5.  This document at present does NOT cover...

  ╖  Compiling the PPP daemon software
     See the documentation that comes with the version of pppd you are
     using.

  ╖  Connecting and configuring a modem to Linux (in detail)
     See the Serial-HOWTO and for modem specific initialisation, see
     Modem Setup Information <http://www.in.net/info/modems/index.html>
     for information that may help you to configure your modem.

  ╖  Using DIP to make PPP connections
     Use chat instead...

  ╖  Using socks or IP Masquerade
     There are perfectly good documents already covering these two
     packages.

  ╖  Using diald to set up an automated connection
     See the diald documentation for information on this.

  ╖  Using EQL to gang together two modems into a single PPP link.

  ╖  Distribution specific PPP connection methods (such as the Red Hat
     4.x network configuration tool.
     See the distribution for documentation on the methods used.

  ╖  The growing number of tools available to automate PPP set up
     See the appropriate documentation.

  4.  Software versions covered

  This HOWTO assumes that you are using a Linux 1.2.x kernel with the
  PPP 2.1.2 software or Linux 1.3.X/2.0.x and PPP 2.2.

  At the time of writing, the latest official version of PPP available
  for Linux is ppp-2.2f. The new version (ppp-2.3) is still in beta.

  It is possible to use PPP 2.2.0 with kernel 1.2.13. This requires
  kernel patches. It is recommended that version 1.2.13 kernel users
  move up to ppp-2.2 as it includes several bug fixes and enhancements.

  Also, you should particularly note that you cannot use the PPP 2.1.2
  software with Linux kernel version 2.0.X.

  Please note that this document does NOT cover problems arising from
  the use of loadable modules for Linux kernel 2.0.x. Please see the
  kerneld mini-HOWTO and the kernel/module 2.0.x documentation (in the
  Linux 2.0.x source tree at /usr/src/linux/Documentation/...).

  As this document is designed to assist new users, it is highly
  recommended that you use a version of the Linux kernel and the
  appropriate PPP version that are known to be stable together.

  5.  Other Useful/Important Documents

  Users are advised to read :-

  ╖  the documentation that comes with the PPP package;

  ╖  the pppd and chat man pages;
     (use man chat and man pppd to explore these)

  ╖  the Linux Network Administration Guide (NAG);
     see The Network Administrators' Guide
     <http://sunsite.unc.edu/mdw/LDP-books/nag-1.0/nag.html>

  ╖  the Net-2/3 HOWTO;
     see Linux NET-2/3-HOWTO
     <http://sunsite.unc.edu/mdw/HOWTO/NET-2-HOWTO.html>
  ╖  Linux kernel documentation installed in
     /usr/src/linux/Documentation when you install the Linux source
     code;

  ╖  The modem setup information page - see Modem Setup Information
     <http://www.in.net/info/modems/index.html>

  ╖  The excellent Unix/Linux books published by O'Reilly and
     Associates. See (O'Reilly and Associates On-Line Catalogue <
     http://www.ora.com/>). If you are new to Unix/Linux, run (don't
     walk) to your nearest computer book shop and invest in a number of
     these immediately!

  ╖  The PPP-FAQ maintained by Al Longyear, available from Linux PPP-FAQ
     <ftp://sunsite.unc.edu/pub/Linux/docs/faqs>.
     This contains a great deal of useful information in question/answer
     format that is very useful when working out why PPP is not working
     (properly).

  ╖  The growing number of Linux books from various publishing houses
     and authors;
     You are actively encouraged to check the currency of these books.
     Linux development and distributions tend to evolve fairly rapidly,
     whilst the revision of books move (generally) much more slowly!
     Buying an excellent book (and there are many) that is now out of
     date will cause new users considerable confusion and frustration.

  The best general starting point for Linux documentation is The Linux
  Documentation Project Home Page <http://sunsite.unc.edu/mdw/>. The
  HOWTO's tend to be revised reasonably regularly.

  Whilst you can use this document to create your PPP link without
  reading any of these documents, you will have a far better
  understanding of what is going on if you do so! You will also be able
  to address problems yourself (or at least ask more intelligent
  questions on the comp.os.linux... newsgroups or Linux mailing lists).

  These documents (as well as various others, including the relevant
  RFCs) provide additional and more detailed explanation than is
  possible in this HOWTO.

  If you are connecting a LAN to the Internet using PPP, you will need
  to know a reasonable amount about TCP/IP networking. In addition to
  the documents above, you will find the O'Reilly books "TCP/IP Network
  Administration" and "Building Internet Firewalls" of considerable
  benefit!

  5.1.  Useful Linux Mailing Lists

  There are many Linux mailing lists that operate as a means of
  communication between users of many levels of ability. By all means
  subscribe to those that interest you and contribute your expertise and
  views.

  A word to the wise: some lists are specifically aimed at "high
  powered" users and/or specific topics. Whilst no-one will complain if
  you 'lurk' (subscribe but don't post messages), you are likely to earn
  heated comments (if not outright flames) if you post 'newbie'
  questions to inappropriate lists.

  This is not because guru level users hate new users, but because these
  lists are there to handle the specific issues at particular levels of
  difficulty.

  By all means join the lists that offer open subscription, but keep
  your comments relevant to the subject of the list!

  A good starting point for Linux mailing lists is Linux Mailing List
  Directory <http://summer.snu.ac.kr/~djshin/linux/mail-
  list/index.shtml>

  6.  Overview of what has to be done to get PPP working as a client

  This document contains a great deal of information - and with each
  version it grows!

  As a consequence, this section aims to provide a concise overview of
  the actions you will need to take to get your Linux system connected
  as a client to a PPP server.

  6.1.  Obtaining/Installing the software

  If your Linux distribution does not include the PPP software, you will
  need to obtain this from the Linux PPP daemon
  <ftp://sunsite.unc.edu/pub/Linux/system/Network/serial/ppp/ppp-2.2.0f.tar.gz>.

  This is the latest official version at the time of writing. However,
  choose the latest version available from this site (ppp-2.3 is in beta
  at the time of writing and should be released soon).

  The PPP package contains instructions on how to compile and install
  the software so this HOWTO does not!

  6.2.  Compiling PPP support into the kernel

  Linux PPP operations come in two parts

  ╖  the PPP daemon mentioned above

  ╖  kernel support for PPP

  Many distributions seem to provide PPP kernel support in their default
  installation kernels, but others do not.

  If at boot your kernel reports messages like

  ______________________________________________________________________
  PPP Dynamic channel allocation code copyright 1995 Caldera, Inc.
  PPP line discipline registered.
  ______________________________________________________________________

  your kernel does have PPP support compiled in.

  That said, you will probably want to compile your own kernel whatever
  your distribution to provide the most efficient use of system
  resources given your particular hardware configuration. It is worth
  remembering that the kernel cannot be swapped out of memory and so
  keeping the kernel as small as possible has advantages on a memory
  limited machine.

  This document provides minimal kernel re-compilation instructions at
  section ``Configuring your Linux Kernel''.

  For greater detail, see the Kernel-HOWTO at The Linux Kernel HOWTO
  <http://sunsite.unc.edu/mdw/HOWTO/Kernel-HOWTO.html>

  6.3.  Obtaining information from your ISP

  There are an almost infinite number of ways in which a PPP server can
  be set up. In order to connect to your ISP (or corporate PPP server to
  access your intranet), you will need to obtain information on how the
  PPP server operates.

  Because you are using Linux, you may have some difficulty with some
  ISP help desks (and work site based PPP intranet servers) which know
  only about MS Windows clients.

  However, a rapidly growing number of ISPs use Linux to provide their
  service - and Linux is also penetrating the corporate environment as
  well, so you may be lucky if you do strike problems.

  Section ``Getting the Information you need about the PPP server''
  tells you what you need to know about the PPP server to which you are
  going to connect - and how to find out the information you need to
  know.

  6.4.  Configuring your modem and serial port

  In order to connect to a PPP server and to obtain the best possible
  data transfer rate, your modem needs to be configured correctly.

  Similarly, the serial ports on your modem and computer need to be set
  up correctly.

  Section ``Configuring your modem and serial port'' provides
  information on this.

  6.5.  Setting up Name to Address Resolution (DNS)

  In addition to the files that run PPP and perform the automated log in
  to the PPP server, there are a number of text configuration files that
  have to be set up for your computer to be able to resolve names like
  www.interweft.com.au to the IP address that is actually used to
  contact that computer. These are:-

  ╖  /etc/resolv.conf

  ╖  /etc/host.conf

  Section ``Setting up Name to Address Resolution'' for details on
  setting this up.

  In particular, you do NOT need to run a name server on your Linux PC
  in order to connect to the Internet (although you may wish to). All
  you need is to know the IP number of at least one name server that you
  can use (preferably one at your ISPs site).

  6.6.  PPP and root Privileges

  As establishing a PPP link between you Linux computer and another PPP
  server requires manipulation of network devices (the PPP interface is
  a network interface) and the kernel routing table, pppd requires root
  privileges.

  For details on this, see section ``Using PPP and root privileges''.

  6.7.  Checking your distribution PPP Files and setting up the PPP
  Options

  There are a number of configuration and dialer files that need to be
  set up to get PPP operational. There are examples as part of the PPP
  distribution and this section shows what files you should have:-

  ______________________________________________________________________
  /etc/ppp/options
  /etc/ppp/scripts/ppp-on
  /etc/ppp/scripts/ppp-on-dialer
  /etc/ppp/options.tpl
  ______________________________________________________________________

  You may need to create some additional files depending on exactly what
  you are aiming to achieve with PPP:-

  ______________________________________________________________________
  /etc/ppp/options.ttyXX
  /etc/ppp/ip-up
  /etc/ppp/pap-secrets
  /etc/ppp/chap-secrets
  ______________________________________________________________________

  In addition, the PPP daemon can use a large number of command line
  options and it is important to use the right ones; so this section
  takes you through the standard PPP options and helps you choose the
  options you should use.

  For details on this, see ``Setting up the PPP connection files''.

  6.8.  If your PPP server uses PAP (Password Authentication Protocol)

  Many ISPs and corporate PPP servers use PAP. If your server does not
  require you to use PAP (if you can log in manually and receive the
  standard user name/password text based prompts it does not use PAP),
  you can safely ignore this section.

  Instead of logging into such a server using a user name and password
  when prompted to enter them by the server, a PPP server using PAP does
  not require a text based login.

  The user authentication information instead is exchanged as part of
  the link control protocol (LCP) which is the first part of
  establishing a PPP link.

  Section ``If your PPP server uses PAP (Password Authentication
  Protocol)'' provides information on the files you need to set up to
  establish a PPP link using PAP.

  6.9.  Connecting to the PPP server by hand

  Having set up the basic files, it is a good idea to test these by
  connecting (using minicom or seyon) and starting pppd on your Linux PC
  by hand.

  See Section ``Setting up the PPP connection manually'' for full
  details of setting this up.

  6.10.  Automating your PPP Connection

  Once you are able to log in by hand, you can now move to setting up a
  set of scripts that will automate the establishment of the connection.

  Section ``Automating your connections - Creating the connection
  scripts'' covers setting up the necessary scripts, with considerable
  attention paid to chat and scripting the login process to the PPP
  server.

  This section discusses scripts for user name/password authentication
  as well as scripts for PAP/CHAP authenticating servers.

  6.11.  Shutting down the link

  Once your link is up and working, you need to be able to deactivate
  the link.

  This is covered in Section ``Shutting down the PPP link''.

  6.12.  If you have problems

  Many people have problems getting PPP to work straight away. The
  variation in PPP servers and how they require you to set up the
  connection is enormous. Similarly, there are many options to PPP - and
  some combinations of these just do not work together, ever.

  In addition to the problems of logging in and starting the PPP
  service, there are problems with the modems and the actual telephone
  lines as well!

  Section ``Fixing problems'' provides some basic information about
  common errors, how to isolate these and fix them.

  This is NOT intended to provide more than just the basics. Al Longyear
  maintains the PPP-FAQ which contains much more information on this
  topic!

  6.13.  After the link comes up

  Once a PPP link is operational (specifically, once the IP layer is
  operational), Linux PPP can automatically run (as the root user), a
  script to perform any function you can write a script to accomplish.

  Section ``After the link comes up'' provides information on the
  /etc/ppp/ip-up script, the parameters it receives from PPP and how to
  use it to do things like acquire your email from your ISP account,
  send any queued email waiting transmission on your machine and such.

  6.14.  Problems with standard IP services on a Dynamic IP number PPP
  link

  As noted in the introduction, dynamic IP numbers affect the ability of
  your Linux PC to act as a server on the Internet.

  Section ``Problems with standard IP services on a Dynamic IP number
  PPP link'' provides information on the (main) services affected and
  what you can do (if anything) to overcome this.

  7.  Configuring your Linux Kernel

  In order to use PPP, your Linux kernel must be compiled to include PPP
  support. Obtain the Linux source code for your kernel if you do not
  already have this - it belongs in /usr/src/linux on Linux's standard
  file system.

  Check out this directory - many Linux distributions install the source
  tree (the files and subdirectories) as part of their installation
  process.

  At bootup, your Linux kernel prints out a great deal of information.
  Amongst this is information about PPP support if the kernel includes
  this. To view this information, look at your syslog file or use dmesg
  | less to display the information to the screen. If your kernel
  includes PPP support, you will see lines like

  ______________________________________________________________________
  PPP Dynamic channel allocation code copyright 1995 Caldera, Inc.
  PPP line discipline registered.
  ______________________________________________________________________

  (this is for the Linux 2.0.x kernel series).

  Linux kernel sources can be obtained by ftp from sunsite.unc.edu or
  its mirror sites.

  7.1.  Installing the Linux Kernel source

  The following are brief instructions for obtaining and installing the
  Linux kernel sources. Full information can be obtained from The Linux
  Kernel HOWTO <http://sunsite.unc.edu/mdw/HOWTO/Kernel-HOWTO.html>.

  In order to install and compile the Linux kernel, you need to be
  logged in as root.

  1. Change directory to the /usr/src directory
     cd /usr/src

  2. Check in /usr/src/linux to see if you already have the sources
     installed.

  3. If you don't have the sources, get them from Linux kernel source
     directory <ftp://sunsite.unc.edu/pub/Linux/kernel/v2.0> or your
     nearest mirror.
     If you are looking for earlier versions of the kernel (such as
     1.2.X), these are kept in Old Linux kernel source directory
     <ftp://sunsite.unc.edu/pub/Linux/kernel/old>.

  4. Choose the appropriate kernel - usually the most recent one
     available is what you are looking for. Retrieve this and put the
     source tar file in /usr/src.
     Note: a 'tar' file is an archive - possibly compressed (as are the
     Linux kernel source tar files) containing many files in a number of
     directories. It is the Linux equivalent of a DOS multi-directory
     zip file.

  5. If you already have the Linux sources installed but are upgrading
     to a new kernel, you must remove the old sources. Use the command
     rm -rf /usr/src/linux

  6. Now uncompress and extract the sources using the command
     tar xzf linux-2.0.XX.tar.gz

  7. Now, cd /usr/src/linux and read the README file. This contains an
     excellent explanation of how to go about configuring and compiling
     a new kernel. Read this file (it's a good idea to print it out and
     have a copy handy whilst you are compiling until you have done this
     enough times to know your way around).

  7.2.  Knowing your hardware

  You MUST know what cards/devices you have inside your PC if you are
  going to recompile your kernel!!! For some devices (such as sound
  cards) you will also need to know various settings (such as IRQ's, I/O
  addresses and such).

  7.3.  Kernel compilation - the Linux 1.2.13 kernel

  To start the configuration process, follow the instructions in the
  README file to properly install the sources. You start the kernel
  configuration process with
       make config

  In order to use PPP, you must configure the kernel to include PPP
  support (PPP requires BOTH pppd AND kernel support for PPP).

  ______________________________________________________________________
    PPP (point-to-point) support (CONFIG_PPP) [n] y
  ______________________________________________________________________

  Answer the other make config questions according to the hardware in
  your PC and the features of the Linux operating system you want. Then
  continue to follow the README to compile and install your new kernel.

  The 1.2.13 kernel creates only 4 PPP devices. For multi- port serial
  cards, you will need to edit the kernel PPP sources to obtain more
  ports. (See the README.linux file that comes as part of the PPP-2.1.2
  distribution for full details of the simple edits you need to make).

  Note: the 1.2.13 configuration dialogue does NOT allow you to go
  backwards - so if you make a mistake in answering one of the questions
  in the make config dialogue, exit by typing CTRL C and start again.

  7.4.  Kernel compilation - the Linux 1.3.x and 2.0.x kernels

  For Linux 1.3.x and 2.0.x, you can use a similar process as for Linux
  1.2.13. Again, follow the instructions in the README file to properly
  install the sources. You start the kernel configuration process with

       make config

  However, you also have the choice of

       make menuconfig

  This provides a menu based configuration system with online help that
  allows you to move backwards and forwards in the configuration
  process.

  There is also a highly recommended X windows based configuration
  interface

  make xconfig

  You can compile PPP support directly into your kernel or as a loadable
  module.

  If you only use PPP some of the time that your Linux machine is
  operating, then compiling PPP support as a loadable module is
  recommended. Using 'kerneld', your kernel will automatically load the
  module(s) required to provide PPP support when you start your PPP link
  process. This saves valuable memory space: no part of the kernel can
  be swapped out of memory, but loadable modules are automatically
  removed if they are not in use.

  To do this, you need to enable loadable module support:-

  ______________________________________________________________________
          Enable loadable module support (CONFIG_MODULES) [Y/n/?] y
  ______________________________________________________________________

  To add PPP kernel support, answer the following question:-

  ______________________________________________________________________
          PPP (point-to-point) support (CONFIG_PPP) [M/n/y/?]
  ______________________________________________________________________

  For a PPP loadable module, answer M, otherwise for PPP compiled in as
  part of the kernel, answer Y.

  Unlike kernel 1.2.13, kernel 2.0.x creates PPP devices on the fly as
  needed and it is not necessary to hack the sources to increase
  available PPP device numbers at all.

  7.5.  Note on PPP-2.2 and /proc/net/dev

  If you are using PPP-2.2, you will find that a side effect of the 'on
  the fly' creation of the PPP devices is that no devices show up if you
  look in the /proc/net file system until a device is created by
  starting up pppd:-

  ______________________________________________________________________
  [hartr@archenland hartr]$ cat /proc/net/dev
  Inter-|   Receive                  |  Transmit
   face |packets errs drop fifo frame|packets errs drop fifo colls carrier
      lo:  92792    0    0    0    0    92792    0    0    0     0    0
    eth0: 621737   13   13    0   23   501621    0    0    0  1309    0
  ______________________________________________________________________

  Once you have one (or more) ppp services started, you will see entries
  such as this (from a ppp server):-
  ______________________________________________________________________
  [root@kepler /root]# cat /proc/net/dev
  Inter-|   Receive                  |  Transmit
   face |packets errs drop fifo frame|packets errs drop fifo colls carrier
      lo: 428021    0    0    0    0   428021    0    0    0     0    0
    eth0:4788257  648  648  319  650  1423836    0    0    0  4623    5
    ppp0:   2103    3    3    0    0     2017    0    0    0     0    0
    ppp1:  10008    0    0    0    0     8782    0    0    0     0    0
    ppp2:    305    0    0    0    0      297    0    0    0     0    0
    ppp3:   6720    7    7    0    0     7498    0    0    0     0    0
    ppp4: 118231  725  725    0    0   117791    0    0    0     0    0
    ppp5:  38915    5    5    0    0    28309    0    0    0     0    0
  ______________________________________________________________________

  7.6.  General kernel config considerations for PPP

  If you are setting up your Linux PC as a PPP server, you must compile
  in IP forwarding support. This is also necessary if you want to use
  Linux to link to LANs together or your LAN to the Internet.

  If you are linking a LAN to the Internet (or linking together two
  LANs), you should be concerned about security. Adding support for IP
  fire walls to the kernel is probably a MUST!

  You will also need this if you want to use IP masquerade to connect a
  LAN that uses any of the above mentioned 'unconnected' IP network
  numbers.

  To enable IP Masquerade and IP fire walling, you MUST answer yes to
  the first question in the make config process:-

  ______________________________________________________________________
  Prompt for development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL)?
  ______________________________________________________________________

  Whilst this may sound a bit off-putting to new users, many users are
  actively using the IP Masquerade and IP fire walling features of the
  Linux 2.0.XX kernel with no problems.

  Once you have installed and rebooted your new kernel, you can start
  configuring and testing your PPP link(s).

  8.  Getting the Information you need about the PPP server

  Before you can establish a PPP connection with a server, you need to
  obtain the following information (from the sysadmin/user support
  people of the PPP server):-

  ╖  The telephone number(s) to dial for the service
     If you are behind a PABX, you also need the PABX number that gives
     you an outside dial tone - this is frequently digit zero (0) or
     nine (9).

  ╖  Does the server use DYNAMIC or STATIC IP numbers?
     If the server uses STATIC IP numbers, then you may need to know
     what IP number to use for your end of the PPP connection. If your
     ISP is providing you with a subnet of valid IP numbers, you will
     need to know the IP numbers you can use and the network mask
     (netmask).

     Most Internet Service Providers use DYNAMIC IP numbers. As
     mentioned above, this has some implications in terms of the
     services you can use.

     However, even if you are using STATIC IP numbers, most PPP servers
     will never (for security reasons) allow the client to specify an IP
     number as this is a security risk. You do still need to know this
     information!

  ╖  What are the IP numbers of the ISPs Domain Name Servers?
     There should be at least two although only one is needed.

     There could be a problem here. The MS Windows 95 PPP setup allows
     the DNS address to be passed to the client as part of its
     connection process. So your ISP (or corporate help desk) may well
     tell you you don't need the IP address of the DNS server(s).

     For Linux, you DO need the address of at least one DNS. The linux
     implementation of PPP does not allow the setting of the DNS IP
     number dynamically at connection time - and quite possibly will
     never do so.

     Note: whilst Linux (as a PPP client) cannot accept the DNS address
     from a server, it can, when acting as a server, pass this
     information to clients using the dns-addr pppd option.

  ╖  Does the server require the use of PAP/CHAP?
     If this is the case you need to know the "id" and "secret" you are
     to use in connecting. (These are probably your user name and
     password at your ISP).

  ╖  Does the server automatically start PPP or do you need to issue any
     commands to start PPP on the server once you are logged in?
     If you must issue a command to start PPP, what is it?

  ╖  Is the server a Microsoft Windows NT system and, if so, is it using
     the MS PAP/CHAP system?
     Many corporate LANs seem to use MS Windows NT this way for
     increased security.

  Carefully note down this information - you are going to use it!

  9.  Configuring your modem and serial port

  You should make sure that your modem is correctly set up and that you
  know which serial port it is connected to.

  Remember:-

  ╖  DOS com1: = Linux /dev/cua0 (and /dev/ttyS0)

  ╖  DOS com2: = Linux /dev/cua1 (and /dev/ttyS1)
     et cetera

  It is also worth remembering that if you have 4 serial ports, the
  standard PC set up is to have com1 and com3 share IRQ4 and com2 and
  com4 share IRQ3.
  If you have devices on standard serial ports that share an IRQ with
  your modem you are going to have problems. You need to make sure that
  your modem serial port is on its own, unique IRQ. Many modern serial
  cards (and better quality motherboard serial ports) allow you to move
  the IRQ of the serial ports around.

  If you are running Linux kernel 2, you can check the in-use IRQs using
  cat /proc/interrupts, which will produce output like

  ______________________________________________________________________
   0:    6766283   timer
   1:      91545   keyboard
   2:          0   cascade
   4:     156944 + serial
   7:     101764   WD8013
  10:     134365 + BusLogic BT-958
  13:          1   math error
  15:    3671702 + serial
  ______________________________________________________________________

  This shows a serial port on IRQ4 (a mouse) and a serial port on IRQ15
  (the permanent modem based PPP link to the Internet. (There is also a
  serial port on com2, IRQ3 and com4 is on IRQ14, but as they are not in
  use, they do not show up).

  Be warned - you need to know what you are doing if you are going to
  play with your IRQs! Not only do you have to open up you computer,
  pull out cards and play with jumpers, but you need to know what is on
  which IRQ.  In my case, this is a totally SCSI based PC, and so I can
  disable the on motherboard IDE interfaces that normally use IRQ14 and
  15!

  You should also remember that if your PC boots other operating
  systems, moving IRQs around may well mean that OS cannot boot properly
  - or at all!

  If you do move your serial ports to non-standard IRQs, then you need
  to tell Linux which IRQ each port is using. This is done using
  setserial and is best done as part of the boot process in rc.local or
  rc.serial which is called from rc.local or as part of the SysV
  initialisation. For the machine illustrated above, the commands used
  are

  ______________________________________________________________________
  /bin/setserial -b /dev/ttyS2 IRQ 11
  /bin/setserial -b /dev/ttyS3 IRQ 15
  ______________________________________________________________________

  However, if you are using serial modules dynamically loaded when
  required by the kerneld process, you cannot set and forget the IRQ etc
  once at boot time. This is because if the serial module is unloaded,
  Linux forgets the special settings.

  So, if you are loading the serial module on demand, you will need to
  reconfigure the IRQs etc each time the module is loaded.
  9.1.  A note about serial ports and speed capabilities

  If you are using a high speed (external) modem (14,400 Baud or above),
  your serial port needs to be capable of handling the throughput that
  such a modem is capable of producing, particularly when the modems are
  compressing the data.

  This requires your serial port to use a modern UART (Universal
  Asynchronous Receiver Transmitter) such as a 16550(A). If you are
  using an old machine (or old serial card), it is quite possible that
  your serial port has only an 8250 UART, which will cause you
  considerable problems when used with a high speed modem.

  Use the command

       setserial -a /dev/ttySx

  to get Linux to report to you the type of UART you have. If you do not
  have a 16550A type UART, invest in a new serial card (available for
  under $50). When you purchase a new card, make sure you can move the
  IRQs around on it!

  Note: the first versions of the 16550 UART chip had an error. This was
  rapidly discovered and a revision of the chip was released - the
  16550A UART. A relatively small number of the faulty chips did however
  get into circulation. It is unlikely that you will encounter one of
  these but you should look for a response that says 16550A,
  particularly on serial cards of some vintage.

  9.2.  Serial Port Names

  Historically, Linux used cuaX devices for dial out and ttySx devices
  for dial in.

  The kernel code that required this was changed in kernel version 2.0.x
  and you should now use ttySx for both dial in and dial out. I
  understand that the cuaX device names may well disappear in future
  kernel versions.

  9.3.  Configuring your modem

  You will need to configure your modem correctly for PPP - to do this
  READ YOUR MODEM MANUAL! Most modems come with a factory default
  setting that selects the options required for PPP. The minimum
  configuration specifies:-

  ╖  Hardware flow control (RTS/CTS) (&K3 on many Hayes modems)

  Other settings (in standard Hayes commands) you should investigate
  are:-

  ╖  E1 Command/usr/src/linux-2.0.27/include/linux/serial.h Echo ON
     (required for chat to operate)

  ╖  Q0 Report result codes (required for chat to operate)

  ╖  S0=0 Auto Answer OFF (unless you want your modem to answer the
     phone)

  ╖  &C1 Carrier Detect ON only after connect

  ╖  &S0 Data Set Ready (DSR) always ON

  ╖  (depends)   Data Terminal Ready

  There is a site offering modem setups for a growing variety of modem
  makes and models at Modem setup information
  <http://www.in.net/info/modems/index.html> which may assist you in
  this.

  It is also worth while investigating how the modem's serial interface
  between your computer and modem operates. Most modern modems allow you
  to run the serial interface at a FIXED speed whilst allowing the
  telephone line interface to change its speed to the highest speed it
  and the remote modem can both handle.

  This is known as split speed operation. If your modem supports this,
  lock the modem's serial interface to its highest available speed
  (usually 115,200 baud but maybe 38,400 baud for 14,400 baud modems).

  Use your communications software (e.g. minicom or seyon) to find out
  about your modem configuration and set it to what is required for PPP.
  Many modems report their current settings in response to AT&V, but you
  should consult your modem manual.

  If you completely mess up the settings, you can return to sanity
  (usually) by issuing an AT&F - return to factory settings.  (For most
  modem modems I have encountered, the factory settings include all you
  need for PPP - but you should check).

  Once you have worked out the modem setup string required write it
  down.  You now have a decision: you can store these settings in your
  modem non-volatile memory so they can be recalled by issuing the
  appropriate AT command. Alternatively you can pass the correct
  settings to your modem as part of the PPP dialing process.

  If you only use your modem from Linux to call into your ISP or
  corporate server, the simplest set up will have you save your modem
  configuration in non-volatile RAM.

  If on the other hand, you modem is used by other applications and
  operating systems, it is safest to pass this information to the modem
  as each call is made so that the modem is guaranteed to be in the
  correct state for the call. (This has the added advantage also of
  recording the modem setup string in case the modem looses  the
  contents of its NV-RAM, which can indeed happen).

  9.4.  Note on Serial Flow Control

  When data is traveling on serial communication lines, it can happen
  that data arrives faster than a computer can handle it (the computer
  may be busy doing something else - remember, Linux is a multi-user,
  multi- tasking operating system). In order to ensure that data is not
  lost (data does not over run in the input buffer and hence get lost),
  some method of controlling the flow of data is necessary.

  There are two ways of doing this on serial lines:-

  ╖  Using hardware signals (Clear To Send/Request to Send - CTS/RTS)

  ╖  Using software signals (control S and control Q, also known as
     XON/XOFF).

  Whilst the latter may be fine for a terminal (text) link, data on a
  PPP link uses all 8 bits - and it is quite probable that somewhere in
  the data there will be data bytes that translate as control S and
  control Q. So, if a modem is set up to use software flow control,
  things can rapidly go berserk!

  For high speed links using PPP (which uses 8 bits of data) hardware
  flow control is vital and it is for this reason that you must use
  hardware flow control.

  9.5.  Testing your modem for dial out

  Now that you have sorted out the serial port and modem settings it is
  a good idea to make sure that these setting do indeed work by dialing
  you ISP and seeing if you can connect.

  Using you terminal communications package (such as minicom), set up
  the modem initialisation required for PPP and dial into the PPP server
  you want to connect to with a PPP session.

  (Note: at this stage we are NOT trying to make a PPP connection - just
  establishing that we have the right phone number and also to find out
  exactly what the server sends to us in order to get logged in and
  start PPP).

  During this process, either capture (log to a file) the entire login
  process or carefully (very carefully) write down exactly what prompts
  the server gives to let you know it is time to enter your user name
  and password (and any other commands needed to establish the PPP
  connection).

  If your server uses PAP, you should not see a login prompt, but should
  instead see the (text representation) of the link control protocol
  (which looks like garbage) starting on your screen.

  A few words of warning:-

  ╖  some servers are quite intelligent: you can log in using text based
     user name/passwords OR using PAP. So if your ISP or corporate site
     uses PAP but you do not see the garbage start up immediately, this
     may not mean you have done something wrong.

  ╖  some servers require you to enter some text initially and then
     start a standard PAP sequence.
  ╖  Some PPP servers are passive - that is they simply sit there
     sending nothing until the client that is dialing in sends them a
     valid lcp packet. If the ppp server you are connecting to operates
     in passive mode, you will never see the garbage!

  ╖  Some servers do not start PPP until you press ENTER - so it is
     worth trying this if you correctly log in and do not see the
     garbage!

  It is worth dialing in at least twice - some servers change their
  prompts (e.g. with the time!) every time you log in. The two critical
  prompts your Linux box needs to be able to identify every time you
  dial in are:-

  ╖  the prompt that requests you to enter your user name;

  ╖  the prompt that requests you to enter your password;

  If you have to issue a command to start PPP on the server, you will
  also need to find out the prompt the server gives you once you are
  logged in to tell you that you can now enter the command to start ppp.

  If your server automatically starts PPP, once you have logged in, you
  will start to see garbage on your screen - this is the PPP server
  sending your machine information to start up and configure the PPP
  connection.

  This should look something like this :-

  ______________________________________________________________________
  ~y}#.!}!}!} }8}!}$}%U}"}&} } } } }%}& ...}'}"}(}"} .~~y}
  ______________________________________________________________________

  (and it just keeps on coming!)

  On some systems PPP must be explicitly started on the server. This is
  usually because the server has been set up to allow PPP logins and
  shell logins using the same user name/password pair. If this is the
  case, issue this command once you have logged in. Again, you will see
  the garbage as the server end of the PPP connection starts up.

  If you do not see this immediately after connecting (and logging in
  and starting the PPP server if required), press Enter to see if this
  starts the PPP server...

  At this point, you can hang up your modem (usually, type +++ quickly
  and then issue the ATHO command once your modem responds with OK).

  If you can't get your modem to work, read your modem manual, the man
  pages for your communications software and the Serial HOWTO! Once you
  have this sorted out, carry on as above.

  10.  Setting up Name to Address Resolution (DNS)

  Whilst we humans like to give names to things, computers really like
  numbers. On a TCP/IP network (which is what the Internet is), we call
  machines by a particular name - and every machine lives in a
  particular "domain". For example, my Linux workstation is called
  archenland and it resides in the interweft.com.au domain. Its human
  readable address is thus archenland.interweft.com.au (which is known
  as the FQDN - fully qualified domain name).

  However, for this machine to be found by other computers on the
  Internet, it is actually known by its IP number when computers are
  communicating across the Internet.

  Translating (resolving) machine (and domain) names into the numbers
  actually used on the Internet is the business of machines that offer
  the Domain Name Service.

  What happens is this:-

  ╖  your machine needs to know the IP address of a particular computer.
     The application requiring this information asks the 'resolver' on
     your Linux PC to provide this information;

  ╖  the resolver queries the local host file (/etc/hosts and/or the
     domain name servers it knows about (the exact behaviour of the
     resolver is determined by /etc/host.conf);

  ╖  if the answer is found in the host file, this answer is returned;

  ╖  if a domain name server is specified, your PC queries this machine;

  ╖  if the DNS machine already knows the IP number for the required
     name, it returns it. If it does not, it queries other name servers
     across the Internet to find the information. The name server than
     passes this information back to the requesting resolver - which
     gives the information to the requesting application.

  When you make a PPP connection, you need to tell your Linux machine
  where it can get host name to IP number (address resolution)
  information so that you can use the machine names but your computer
  can translate these to the IP numbers it needs to do its work.

  One way is to enter every host that you want to talk to into the
  /etc/hosts file (which is in reality totally impossible if you are
  connecting to the Internet); another is to use the machine IP numbers
  as opposed to the names (an impossible memory task for all but the
  smallest LANs).

  The best way is to set up Linux so that it knows where to go to get
  this name to number information - automatically. This service is
  provided by the Domain Name Server (DNS) system. All that is necessary
  is to enter the IP number(s) for the domain name servers into your
  /etc/resolv.conf file.

  10.1.  The /etc/resolv.conf file

  Your PPP server sysadmin/user support people should provide you with
  two DNS IP numbers (only one is necessary - but two gives some
  redundancy in the event of failure).

  As previously mentioned, Linux cannot set its name server IP number in
  the way that MS Windows 95 does. So you must insist (politely) that
  your ISP provide you with this information!

  Your /etc/resolv.conf should look something like :-

  ______________________________________________________________________
  domain your.isp.domain.name
  nameserver 10.25.0.1
  nameserver 10.25.1.2
  ______________________________________________________________________

  Edit this file (creating it if necessary) to represent the information
  that your ISP has provided. It should have ownership and permissions
  as follows :-

       -rw-r--r--   1 root     root           73 Feb 19 01:46 /etc/resolv.conf

  If you have already set up a /etc/resolv.conf because you are on a
  LAN, simply add the IP numbers of the PPP DNS servers to your existing
  file.

  10.2.  The /etc/host.conf file

  You should also check that your /etc/host.conf file is correctly set
  up. This should look like

  ______________________________________________________________________
  order hosts,bind
  multi on
  ______________________________________________________________________

  This tells the resolver to use information in the host file before it
  sends queries to the DNS for resolution.

  11.  Using PPP and root privileges

  Because PPP needs to set up networking devices, change the kernel
  routing table and so forth, it requires root privileges to do this.

  If users other than root are to set up PPP connections, the pppd
  program should be setuid root :-
       -rwsr-xr-x   1 root     root        95225 Jul 11 00:27 /usr/sbin/pppd

  If /usr/sbin/pppd is not set up this way, then as root issue the
  command:-

       chmod u+s /usr/sbin/pppd

  What this does is make pppd run with root privileges even if the
  binary is run by an ordinary user. This allows a normal user to run
  pppd with the necessary privileges to set up the network interfaces
  and the kernel routing table.

  Programs that run 'set uid root' are potential security holes and you
  should be extremely cautious about making programs 'suid root'. A
  number of programs (including pppd) have been carefully written to
  minimise the danger of running suid root, so you should be safe with
  this one (but no guarantees).

  Depending on how you want your system to operate - specifically if you
  want ANY user on your system to be able to initiate a PPP link, you
  should make your ppp-on/off scripts world read/execute. (This is
  probably fine if your PC is used ONLY by you).

  However, if you do NOT want just anyone to be able to start up a PPP
  connection (for example, your children have accounts on your Linux PC
  and you do not want them hooking into the Internet without your
  supervision), you will need to establish a PPP group (as root, edit
  /etc/group) and :-

  ╖  Make pppd suid root, owned by user root and group PPP, with the
     'other' permissions on this file empty. It should then look like

       -rwsr-x---   1 root     PPP        95225 Jul 11 00:27 /usr/sbin/pppd

  ╖  Make the ppp-on/off scripts owned by user root and group PPP

  ╖  Make the ppp-on/off scripts read/executable by group PPP

         -rwxr-x---   1 root     PPP           587 Mar 14  1995 /usr/sbin/ppp-on
         -rwxr-x---   1 root     PPP           631 Mar 14  1995 /usr/sbin/ppp-off

  ╖  Make the other access rights for ppp-on/off nill.

  ╖  add the users who will be firing up PPP to the PPP group in
     /etc/group

  Even if you do this, ordinary users will STILL not be able to shut
  down the link under software control! Running the ppp-off script
  requires root privileges. However, any user can just turn off the
  modem (or disconnect the telephone line from an internal modem).

  An alternative (and better method) to this set up is to use the sudo
  program. This offers superior security and will allow you to set
  things up so that any (authorised) user can activate/deactivate the
  link using the scripts. Using sudo will allow an authorised user to
  activate/deactivate the PPP link cleanly and securely.

  12.  Setting up the PPP connection files

  You now need to be logged in as root to create the directories and
  edit the files needed to set up PPP, even if you want PPP to be
  accessible to all users.

  PPP uses a number of files to connect and set up a PPP connection.
  These differ in name and location between PPP 2.1.2 and 2.2.

  For PPP 2.1.2 the files are:-

  ______________________________________________________________________
  /usr/sbin/pppd          # the PPP binary
  /usr/sbin/ppp-on        # the dialer/connection script
  /usr/sbin/ppp-off       # the disconnection script
  /etc/ppp/options        # the options pppd uses for all connections
  /etc/ppp/options.ttyXX  # the options specific to a connection on this port
  ______________________________________________________________________

  For PPP 2.2 the files are:-

  ______________________________________________________________________
  /usr/sbin/pppd                  # the PPP binary
  /etc/ppp/scripts/ppp-on         # the dialer/connection script
  /etc/ppp/scripts/ppp-on-dialer  # part 1 of the dialer script
  /etc/ppp/scripts/ppp-off        # the actual chat script itself
  /etc/ppp/options                # the options pppd uses for all connections
  /etc/ppp/options.ttyXX          # the options specific to a connection on this port
  ______________________________________________________________________

  Red Hat Linux users should note that the standard Red Hat 4.X
  installation places these scripts in /usr/doc/ppp-2.2.0f-2/scripts.

  In your /etc directory there should be a ppp directory:-

       drwxrwxr-x   2 root     root         1024 Oct  9 11:01 ppp

  If it does not exist - create it with these ownerships and
  permissions.

  If the directory already existed, it should contain a template options
  file called options.tpl. This file is included below in case it does
  not.

  Print it out as it contains an explanation of nearly all the PPP
  options (these are useful to read in conjunction with the pppd man
  pages).  Whilst you can use this file as the basis of your
  /etc/ppp/options file, it is probably better to create your own
  options file that does not include all the comments in the template -
  it will be much shorter and easier to read/maintain.

  If you have multiple serial lines/modems (typically the case for PPP
  servers), create a general /etc/ppp/options file containing the
  options that are common for all the serial ports on which you are
  supporting dial in/out  and set up individual option files for each
  serial line on which you will be establishing a PPP connection with
  the individual settings required for each port.

  These port specific option files are named options.ttyx1,
  options.ttyx2 and so forth (where x is the appropriate letter for your
  serial ports).

  However, for a single PPP connection, you can happily use the
  /etc/ppp/options file. Alternatively, you can put all the options as
  arguments in the pppd command itself.

  It is easier to maintain a setup that uses /etc/ppp/options.ttySx
  files. If you use PPP to connect to a number of different sites, you
  can create option files for each site in /etc/ppp/options.site and
  then specify the option file as a parameter to the PPP command as you
  connect (using the file option-file pppd option to pppd on the command
  line).

  12.1.  The supplied options.tpl file

  Some distributions of PPP seem to have lost the options.tpl file, so
  here is the complete file. I suggest that you do NOT edit this file to
  create your /etc/ppp/options file(s). Rather, copy this to a new file
  and then edit that. If you mess up your edits, you can then go back to
  the original and start again.

  ______________________________________________________________________
  # /etc/ppp/options -*- sh -*- general options for pppd
  # created 13-Jul-1995 jmk
  # autodate: 01-Aug-1995
  # autotime: 19:45

  # Use the executable or shell command specified to set up the serial
  # line.  This script would typically use the "chat" program to dial the
  # modem and start the remote ppp session.
  #connect "echo You need to install a connect command."

  # Run the executable or shell command specified after pppd has
  # terminated the link.  This script could, for example, issue commands
  # to the modem to cause it to hang up if hardware modem control signals
  # were not available.
  #disconnect "chat -- \d+++\d\c OK ath0 OK"

  # async character map -- 32-bit hex; each bit is a character
  # that needs to be escaped for pppd to receive it.  0x00000001
  # represents '\x01', and 0x80000000 represents '\x1f'.
  #asyncmap 0

  # Require the peer to authenticate itself before allowing network
  # packets to be sent or received.
  #auth

  # Use hardware flow control (i.e. RTS/CTS) to control the flow of data
  # on the serial port.
  #crtscts

  # Use software flow control (i.e. XON/XOFF) to control the flow of data
  # on the serial port.
  #xonxoff

  # Add a default route to the system routing tables, using the peer as
  # the gateway, when IPCP negotiation is successfully completed.  This
  # entry is removed when the PPP connection is broken.
  #defaultroute

  # Specifies that certain characters should be escaped on transmission
  # (regardless of whether the peer requests them to be escaped with its
  # async control character map).  The characters to be escaped are
  # specified as a list of hex numbers separated by commas.  Note that
  # almost any character can be specified for the escape option, unlike
  # the asyncmap option which only allows control characters to be
  # specified.  The characters which may not be escaped are those with hex
  # values 0x20 - 0x3f or 0x5e.
  #escape 11,13,ff

  # Don't use the modem control lines.
  #local

  # Specifies that pppd should use a UUCP-style lock on the serial device
  # to ensure exclusive access to the device.
  #lock

  # Use the modem control lines.  On Ultrix, this option implies hardware
  # flow control, as for the crtscts option.  (This option is not fully
  # implemented.)
  #modem

  # Set the MRU [Maximum Receive Unit] value to <n> for negotiation.  pppd
  # will ask the peer to send packets of no more than <n> bytes. The
  # minimum MRU value is 128.  The default MRU value is 1500.  A value of
  # 296 is recommended for slow links (40 bytes for TCP/IP header + 256
  # bytes of data).
  #mru 542

  # Set the interface netmask to <n>, a 32 bit netmask in "decimal dot"
  # notation (e.g. 255.255.255.0).
  #netmask 255.255.255.0

  # Disables the default behaviour when no local IP address is specified,
  # which is to determine (if possible) the local IP address from the
  # hostname. With this option, the peer will have to supply the local IP
  # address during IPCP negotiation (unless it specified explicitly on the
  # command line or in an options file).
  #noipdefault

  # Enables the "passive" option in the LCP.  With this option, pppd will
  # attempt to initiate a connection; if no reply is received from the
  # peer, pppd will then just wait passively for a valid LCP packet from
  # the peer (instead of exiting, as it does without this option).
  #passive

  # With this option, pppd will not transmit LCP packets to initiate a
  # connection until a valid LCP packet is received from the peer (as for
  # the "passive" option with old versions of pppd).
  #silent

  # Don't request or allow negotiation of any options for LCP and IPCP
  # (use default values).
  #-all

  # Disable Address/Control compression negotiation (use default, i.e.
  # address/control field disabled).
  #-ac

  # Disable asyncmap negotiation (use the default asyncmap, i.e. escape
  # all control characters).
  #-am

  # Don't fork to become a background process (otherwise pppd will do so
  # if a serial device is specified).
  #-detach

  # Disable IP address negotiation (with this option, the remote IP
  # address must be specified with an option on the command line or in an
  # options file).
  #-ip

  # Disable magic number negotiation.  With this option, pppd cannot
  # detect a looped-back line.
  #-mn

  # Disable MRU [Maximum Receive Unit] negotiation (use default, i.e.
  # 1500).
  #-mru

  # Disable protocol field compression negotiation (use default, i.e.
  # protocol field compression disabled).
  #-pc

  # Require the peer to authenticate itself using PAP.
  # This requires TWO WAY authentication - do NOT use this for a standard
  # PAP authenticated link to an ISP as this will require the ISP machine
  # to authenticate itself to your machine (and it will not be able to).
  #+pap

  # Don't agree to authenticate using PAP.
  #-pap

  # Require the peer to authenticate itself using CHAP [Cryptographic
  # Handshake Authentication Protocol] authentication.
  # This requires TWO WAY authentication - do NOT use this for a standard
  # CHAP authenticated link to an ISP as this will require the ISP machine
  # to authenticate itself to your machine (and it will not be able to).
  #+chap

  # Don't agree to authenticate using CHAP.
  #-chap

  # Disable negotiation of Van Jacobson style IP header compression (use
  # default, i.e. no compression).
  #-vj

  # Increase debugging level (same as -d).  If this option is given, pppd
  # will log the contents of all control packets sent or received in a
  # readable form.  The packets are logged through syslog with facility
  # daemon and level debug. This information can be directed to a file by
  # setting up /etc/syslog.conf appropriately (see syslog.conf(5)).  (If
  # pppd is compiled with extra debugging enabled, it will log messages
  # using facility local2 instead of daemon).
  #debug

  # Append the domain name <d> to the local host name for authentication
  # purposes.  For example, if gethostname() returns the name porsche,
  # but the fully qualified domain name is porsche.Quotron.COM, you would
  # use the domain option to set the domain name to Quotron.COM.
  #domain <d>

  # Enable debugging code in the kernel-level PPP driver.  The argument n
  # is a number which is the sum of the following values: 1 to enable
  # general debug messages, 2 to request that the contents of received
  # packets be printed, and 4 to request that the contents of transmitted
  # packets be printed.
  #kdebug n

  # Set the MTU [Maximum Transmit Unit] value to <n>. Unless the peer
  # requests a smaller value via MRU negotiation, pppd will request that
  # the kernel networking code send data packets of no more than n bytes
  # through the PPP network interface.
  #mtu <n>

  # Set the name of the local system for authentication purposes to <n>.
  # This will probably have to be set to your ISP user name if you are
  # using PAP/CHAP.
  #name <n>

  # Set the user name to use for authenticating this machine with the peer
  # using PAP to <u>.
  # Do NOT use this if you are using 'name' above!
  #user <u>

  # Enforce the use of the host name as the name of the local system for
  # authentication purposes (overrides the name option).
  #usehostname

  # Set the assumed name of the remote system for authentication purposes
  # to <n>.
  #remotename <n>

  # Add an entry to this system's ARP [Address Resolution Protocol]
  # table with the IP address of the peer and the Ethernet address of this
  # system.
  #proxyarp

  # Use the system password database for authenticating the peer using
  # PAP.
  #login

  # If this option is given, pppd will send an LCP echo-request frame to
  # the peer every n seconds. Under Linux, the echo-request is sent when
  # no packets have been received from the peer for n seconds. Normally
  # the peer should respond to the echo-request by sending an echo-reply.
  # This option can be used with the lcp-echo-failure option to detect
  # that the peer is no longer connected.
  #lcp-echo-interval <n>

  # If this option is given, pppd will presume the peer to be dead if n
  # LCP echo-requests are sent without receiving a valid LCP echo-reply.
  # If this happens, pppd will terminate the connection.  Use of this
  # option requires a non-zero value for the lcp-echo-interval parameter.
  # This option can be used to enable pppd to terminate after the physical
  # connection has been broken (e.g., the modem has hung up) in
  # situations where no hardware modem control lines are available.
  #lcp-echo-failure <n>

  # Set the LCP restart interval (retransmission timeout) to <n> seconds
  # (default 3).
  #lcp-restart <n>

  # Set the maximum number of LCP terminate-request transmissions to <n>
  # (default 3).
  #lcp-max-terminate <n>

  # Set the maximum number of LCP configure-request transmissions to <n>
  # (default 10).
  # Some PPP servers are slow to start up. You may need to increase this
  # if you keep getting 'serial line looped back' errors and your are SURE
  # that you have logged in correctly and PPP should be starting on the server.
  #lcp-max-configure <n>

  # Set the maximum number of LCP configure-NAKs returned before starting
  # to send configure-Rejects instead to <n> (default 10).
  #lcp-max-failure <n>

  # Set the IPCP restart interval (retransmission timeout) to <n>
  # seconds (default 3).
  #ipcp-restart <n>

  # Set the maximum number of IPCP terminate-request transmissions to <n>
  # (default 3).
  #ipcp-max-terminate <n>

  # Set the maximum number of IPCP configure-request transmissions to <n>
  # (default 10).
  #ipcp-max-configure <n>

  # Set the maximum number of IPCP configure-NAKs returned before starting
  # to send configure-Rejects instead to <n> (default 10).
  #ipcp-max-failure <n>

  # Set the PAP restart interval (retransmission timeout) to <n> seconds
  # (default 3).
  #pap-restart <n>

  # Set the maximum number of PAP authenticate-request transmissions to
  # <n> (default 10).
  #pap-max-authreq <n>

  # Set the CHAP restart interval (retransmission timeout for
  # challenges) to <n> seconds (default 3).
  #chap-restart <n>
  # Set the maximum number of CHAP challenge transmissions to <n>
  # (default 10).
  #chap-max-challenge

  # If this option is given, pppd will re-challenge the peer every <n>
  # seconds.
  #chap-interval <n>

  # With this option, pppd will accept the peer's idea of our local IP
  # address, even if the local IP address was specified in an option.
  #ipcp-accept-local

  # With this option, pppd will accept the peer's idea of its (remote) IP
  # address, even if the remote IP address was specified in an option.
  #ipcp-accept-remote
  ______________________________________________________________________

  12.2.  What options should I use? (No PAP/CHAP)

  Well, as in all things that depends (sigh). The options specified here
  should work with most servers.

  However, if it does NOT work, READ THE TEMPLATE FILE
  (/etc/ppp/options.tpl) and the pppd man pages and speak to the
  sysadmin/user support people who run the server to which you are
  connecting.

  You should also note that the connect scripts presented here also use
  some command line options to pppd to make things a bit easier to
  change.

  ______________________________________________________________________
  # /etc/ppp/options (NO PAP/CHAP)
  #
  # Prevent pppd from forking into the background
  -detach
  #
  # use the modem control lines
  modem
  # use uucp style locks to ensure exclusive access to the serial device
  lock
  # use hardware flow control
  crtscts
  # create a default route for this connection in the routing table
  defaultroute
  # do NOT set up any "escaped" control sequences
  asyncmap 0
  # use a maximum transmission packet size of 552 bytes
  mtu 552
  # use a maximum receive packet size of 552 bytes
  mru 552
  #
  #-------END OF SAMPLE /etc/ppp/options (no PAP/CHAP)
  ______________________________________________________________________

  13.  Protocol) If your PPP server uses PAP (Password Authentication

  If the server to which you are connecting requires PAP or CHAP
  authentication, you have a little bit more work.

  To the above options file, add the following lines

  ______________________________________________________________________
  #
  # force pppd to use your ISP user name as your 'host name' during the
  # authentication process
  name <your ISP user name>       # you need to edit this line
  #
  # If you are running a PPP *server* and need to force PAP or CHAP
  # uncomment the appropriate one of the following lines. Do NOT use
  # these is you are a client connecting to a PPP server (even if it uses PAP
  # or CHAP) as this tells the SERVER to authenticate itself to your
  # machine (which almost certainly can't do - and the link will fail).
  #+chap
  #+pap
  #
  # If you are using ENCRYPTED secrets in the /etc/ppp/pap-secrets
  # file, then uncomment the following line.
  # Note: this is NOT the same as using MS encrypted passwords as can be
  # set up in MS RAS on Windows NT.
  #+papcrypt
  ______________________________________________________________________

  13.1.  Using MSCHAP

  Microsoft Windows NT RAS can be set up to use a variation on CHAP
  (Challenge/Handshake Authentication Protocol). In your PPP sources tar
  ball, you will find a file called README.MSCHAP80 that discusses this.

  You can determine if the server is requesting authentication using
  this protocol by enabling debugging for pppd. If the server is
  requesting MS CHAP authentication, you will see lines like

  ______________________________________________________________________
  rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <auth chap 80> <magic 0x46a3>]
  ______________________________________________________________________

  The critical information here is auth chap 80.

  In order to use MS CHAP, you will need to recompile pppd to support
  this. Please see the instructions in the README.MSCHAP80 file in the
  PPP source file for instructions on how to compile and use this
  variation.

  You should note that at present this code supports only Linux PPP
  clients connecting to an MS Windows NT server. It does NOT support
  setting up a Linux PPP server to use MSCHAP80 authentication from
  clients.

  13.2.  The PAP/CHAP secrets file

  If you are using pap or chap authentication, then you also need to
  create the secrets file. These are:

  ______________________________________________________________________
  /etc/ppp/pap-secrets
  /etc/ppp/chap-secrets
  ______________________________________________________________________

  They must be owned by user root, group root and have file permissions
  740 for security.

  The first point to note about PAP and CHAP is that they are designed
  to authenticate computer systems not users.

  "Huh? What's the difference?" I hear you ask.

  Well now, once your computer has made its PPP connection to the
  server, ANY user on your system can use that connection - not just
  you.  This is why you can set up a WAN (wide area network) link that
  joins two LANs (local area networks) using PPP.

  PAP can (and for CHAP DOES) require bidirectional authentication -
  that is a valid name and secret is required on each computer for the
  other computer involved. However, this is NOT the way most PPP servers
  offering dial up PPP PAP-authenticated connections operate.

  That being said, your ISP will probably have given you a user name and
  password to allow you to connect to their system and thence the
  Internet. Your ISP is not interested in your computer's name at all,
  so you will probably need to use the user name at your ISP as the name
  for your computer.

  This is done using the name user name option to pppd. So, if you are
  to use the user name given you by your ISP, add the line

  ______________________________________________________________________
  name your_user name_at_your_ISP
  ______________________________________________________________________

  to your /etc/ppp/options file.

  Technically, you should really use user our_user name_at_your_ISP for
  PAP, but pppd is sufficiently intelligent to interpret name as user if
  it is required to use PAP. The advantage of using the name option is
  that this is also valid for CHAP.

  As PAP is for authenticating computers, technically you need also to
  specify a remote computer name. However, as most people only have one
  ISP, you can use a wild card (*) for the remote host name in the
  secrets file.

  It is also worth noting that many ISPs operate multiple modem banks
  connected to different terminal servers - each with a different name,
  but ACCESSED from a single (rotary) dial in number. It can therefore
  be quite difficult in some circumstances to know ahead of time what
  the name of the remote computer is, as this depends on which terminal
  server you connect to!

  13.3.  The PAP secrets file

  The /etc/ppp/pap-secrets file looks like

  ______________________________________________________________________
  # Secrets for authentication using PAP
  # client        server       secret     acceptable_local_IP_addresses
  ______________________________________________________________________

  The four fields are white space delimited and the last one can be
  blank (which is what you want for a dynamic and probably static IP
  allocation from your ISP).

  Suppose your ISP gave you a user name of fred and a password of
  flintstone you would set the name fred option in
  /etc/ppp/options[.ttySx] and set up your /etc/ppp/pap-secrets file as
  follows

  ______________________________________________________________________
  # Secrets for authentication using PAP
  # client        server  secret          acceptable local IP addresses
  fred            *       flintstone
  ______________________________________________________________________

  This says for the local machine name fred (which we have told pppd to
  use even though it is not our local machine name) and for ANY server,
  use the password (secret) of flintstone.

  Note that we do not need to specify a local IP address, unless we are
  required to FORCE a particular local, static IP address. Even if you
  try this, it is unlikely to work as most PPP servers (for security
  reasons) do not allow the remote system to set the IP number they are
  to be given.

  13.4.  The CHAP secrets file

  This requires that you have mutual authentication methods - that is
  you must allow for both your machine to authenticate the remote server
  AND the remote server to authenticate your machine.

  So, if your machine is fred and the remote is barney, your machine
  would set name fred remotename barney and the remote machine would set
  name barney remotename fred in their respective /etc/ppp/options.ttySx
  files.

  The /etc/chap-secrets file for fred would look like

  ______________________________________________________________________
  # Secrets for authentication using CHAP
  # client        server  secret            acceptable local IP addresses
  fred            barney  flintstone
  barney          fred    wilma
  ______________________________________________________________________

  and for barney

  ______________________________________________________________________
  # Secrets for authentication using CHAP
  # client        server  secret            acceptable local IP addresses
  barney          fred    flintstone
  fred            barney  wilma
  ______________________________________________________________________

  Note in particular that both machines must have entries for
  bidirectional authentication. This allows the local machine to
  authenticate itself to the remote AND the remote machine to
  authenticate itself to the local machine.

  13.5.  Handling multiple PAP-authenticated connections

  Some users have more than one server to which they connect that use
  PAP.  Provided that your user name is different on each machine to
  which you want to connect, this is not a problem.

  However, many users have the same user name on two (or more - even
  all) systems to which they connect. This then presents a problem in
  correctly selecting the appropriate line from /etc/ppp/pap-secrets.

  As you might expect, PPP provides a mechanism for overcoming this. PPP
  allows you to set an 'assumed name' for the remote (server) end of the
  connection using the remotename option to pppd.

  Let us suppose that you connect to two PPP servers using the username
  fred. You set up your /etc/ppp/pap-secrets something like

  ______________________________________________________________________
  fred    pppserver1      barney
  fred    pppserver2      wilma
  ______________________________________________________________________

  Now, to set connect to pppserver1 you would use name fred remotename
  pppserver1 in your ppp-options and for pppserver2 name fred remotename
  pppserver2.

  As you can select the ppp options file to use with pppd using the file
  filename option, you can set up a script to connect to each of your
  PPP servers, correctly picking the options file to use and hence
  selecting the right remotename option.

  14.  Setting up the PPP connection manually

  Now that you have created your /etc/ppp/options and /etc/resolv.conf
  files (and, if necessary, the /etc/ppp/pap|chap-secrets file), you can
  test the settings by manually establishing a PPP connection. (Once we
  have the manual connection working, we will automate the process).

  To do this, your communications software must be capable of quitting
  WITHOUT resetting the modem. Minicom can do this - ALT Q (or in older
  version of minicom CTRL A Q)

  Make sure you are logged in as root.

  Fire up you communications software (such as minicom), dial into the
  PPP server and log in as normal. If you need to issue a command to
  start up PPP on the server, do so. You will now see the garbage you
  saw before.

  If you are using pap or chap, then merely connecting to the remote
  system should start ppp on the remote and you will see the garbage
  without logging in (although this may not happen for some servers -
  try pressing Enter and see if the garbage starts up).

  Now quit the communications software without resetting the modem (ALT
  Q or CTL A Q in minicom) and at the Linux prompt (as root) type

  ______________________________________________________________________
  pppd -d -detach /dev/ttySx 38400 &
  ______________________________________________________________________

  The -d option turns on debugging - the ppp connection start up
  conversation will be logged to your system log - which is useful if
  you are having trouble.

  Your modem lights should now flash as the PPP connection is
  established.  It will take a short while for the PPP connection to be
  made.

  At this point you can look at the PPP interface, by issuing the
  command

  ______________________________________________________________________
  ifconfig
  ______________________________________________________________________

  In addition to any Ethernet and loop back devices you have, you should
  see something like :-

  ______________________________________________________________________
  ppp0     Link encap:Point-Point Protocol
           inet addr:10.144.153.104  P-t-P:10.144.153.51 Mask:255.255.255.0
           UP POINTOPOINT RUNNING  MTU:552  Metric:1
           RX packets:0 errors:0 dropped:0 overruns:0
           TX packets:0 errors:0 dropped:0 overruns:0
  ______________________________________________________________________

  Where

  ╖  inet addr:10.144.153.10 is the IP number of your end of the link.

  ╖  P-t-P:10.144.153.5 is the SERVER's IP number.

  (Naturally, ifconfig will not report these IP numbers, but the ones
  used by your PPP server.)

  Note: ifconfig also tells you that the link is UP and RUNNING!

  If you get no ppp device listed or something like

  ______________________________________________________________________
  ppp0     Link encap:Point-Point Protocol
           inet addr:0.0.0.0  P-t-P:0.0.0.0  Mask:0.0.0.0
           POINTOPOINT  MTU:1500  Metric:1
           RX packets:0 errors:0 dropped:0 overruns:0
           TX packets:0 errors:0 dropped:0 overruns:0
  ______________________________________________________________________

  Your PPP connection has not been made...see the later section on
  debugging!

  You should also be able to see a route to the the remote host (and
  beyond). To do this, issue the command

  ______________________________________________________________________
  route -n
  ______________________________________________________________________

  You should se something like:-

  ______________________________________________________________________
  Kernel routing table
  Destination     Gateway         Genmask         Flags MSS    Window Use Iface
  10.144.153.3    *               255.255.255.255 UH    1500   0        1 ppp0
  127.0.0.0       *               255.0.0.0       U     3584   0       11 lo
  10.0.0.0        *               255.0.0.0       U     1500   0       35 eth0
  default         10.144.153.3    *               UG    1500   0        5 ppp0
  ______________________________________________________________________

  Of particular importance here, notice we have TWO entries pointing to
  our ppp interface.

  The first is a HOST route (indicated by the H flag) and that allows us
  to see the host to which we are connected to - but no further.

  The second is the default route (established by giving pppd the option
  defaultroute. This is the route that tells our Linux PC to send any
  packets NOT destined for the local Ethernet(s) - to which we have
  specific network routes - to the PPP server itself. The PPP server
  then is responsible for routing our packets out onto the Internet and
  routing the return packets back to us.

  If you do not see a routing table with two entries, something is
  wrong.  In particular if your syslog shows a message telling you pppd
  is not replacing an existing default route, then you have a default
  route pointing at your Ethernet interface - which MUST be replaced by
  a specific network route: YOU CAN ONLY HAVE ONE DEFAULT ROUTE!!!

  You will need to explore your system initialisation files to find out
  where this default route is being set up (it will use a route add
  default... command). Change this command to something like route add
  net....

  Now test the link by 'pinging' the server at its IP number as reported
  by the ifconfig output, i.e.

  ______________________________________________________________________
  ping 10.144.153.51
  ______________________________________________________________________

  You should receive output like

  ______________________________________________________________________
  PING 10.144.153.51 (10.144.153.51): 56 data bytes
  64 bytes from 10.144.153.51: icmp_seq=0 ttl=255 time=328.3 ms
  64 bytes from 10.144.153.51: icmp_seq=1 ttl=255 time=190.5 ms
  64 bytes from 10.144.153.51: icmp_seq=2 ttl=255 time=187.5 ms
  64 bytes from 10.144.153.51: icmp_seq=3 ttl=255 time=170.7 ms
  ______________________________________________________________________

  This listing will go on for ever - to stop it press CTRL C, at which
  point you will receive some more information :-

  ______________________________________________________________________
  --- 10.144.153.51 ping statistics ---
  4 packets transmitted, 4 packets received, 0% packet loss
  round-trip min/avg/max = 170.7/219.2/328.3 ms
  ______________________________________________________________________

  So far so good.

  Now try pinging a host by name (not the name of the PPP server itself)
  but a host at another site that you KNOW is probably going to be up
  and running...). For example

  ______________________________________________________________________
  ping sunsite.unc.edu
  ______________________________________________________________________

  This time there will be a bit of a pause as Linux obtains the IP
  number for the fully qualified host name you have 'ping'ed from the
  DNS you specified in /etc/resolv.conf - so don't worry (but you will
  see your modem lights flash). Shortly you will receive output like

  ______________________________________________________________________
   PING sunsite.unc.edu (152.2.254.81): 56 data bytes
  64 bytes from 152.2.254.81: icmp_seq=0 ttl=254 time=190.1 ms
  64 bytes from 152.2.254.81: icmp_seq=1 ttl=254 time=180.6 ms
  64 bytes from 152.2.254.81: icmp_seq=2 ttl=254 time=169.8 ms
  64 bytes from 152.2.254.81: icmp_seq=3 ttl=254 time=170.6 ms
  64 bytes from 152.2.254.81: icmp_seq=4 ttl=254 time=170.6 ms
  ______________________________________________________________________

  Again, stop the output by pressing CTRL C and get the statistics...

  ______________________________________________________________________
  --- sunsite.unc.edu ping statistics ---
  5 packets transmitted, 5 packets received, 0% packet loss
  round-trip min/avg/max = 169.8/176.3/190.1 ms
  ______________________________________________________________________

  If you don't get any response, try pinging the IP address of the DNS
  server at your ISP's site. If you get a result from this, then it
  looks like you have a problem with /etc/resolv.conf.

  If this doesn't work, you have a routing problem, or your ISP has a
  problem routing packets back to you. Check your routing table as shown
  above and if that is OK, contact your ISP. A good test of the ISP is
  to use another operating system to connect. If you can get beyond your
  ISP with that, then the problem is at your end.

  If everything works, shut down the connection by typing

  ______________________________________________________________________
  ppp-off
  ______________________________________________________________________

  After a short pause, the modem should hang itself up.

  If that does not work, either turn off your modem or fire up your
  communications software and interrupt the modem with +++ and then hang
  up with ATH0 when you receive the modem's OK prompt.

  You may also need to clean up the lock file created by pppd

  ______________________________________________________________________
  rm -f /var/lock/LCK..ttySx
  ______________________________________________________________________

  15.  Automating your connections - Creating the connection scripts

  Whilst you can continue to log in by hand as shown above, it is much
  neater to set up some scripts to do this automatically for you.

  A set of scripts automates the log in and PPP start up so all you have
  to do (as root or as a member of the PPP group) is issue a single
  command to fire up your connection.

  15.1.  Connection scripts for User name/Password Authentication

  If your ISP does NOT require the use of PAP/CHAP, these are the
  scripts for you!

  If the ppp package installed correctly, you should have two example
  files.  For PPP 2.1.2 they are in /usr/sbin and for PPP 2.2 they are
  in /etc/ppp/scripts. They are called

  for PPP-2.1.2

       ppp-on
       ppp-off

  and for PPP-2.2

       ppp-off
       ppp-on
       ppp-on-dialer

  Now, if you are using PPP 2.1.2, I strongly urge you to delete the
  sample files. There are potential problems with these - and don't tell
  me they work fine - I used them for ages too (and recommended them in
  the first version of this HOWTO)!

  For the benefit of PPP 2.1.2 users, here are BETTER template versions,
  taken from the PPP 2.2 distribution. I suggest you copy and use these
  scripts instead of the old PPP-2.1.2 scripts.

  15.2.  The ppp-on script

  This is the first of a PAIR of scripts that actually fire up the
  connection.

  ______________________________________________________________________
  #!/bin/sh
  #
  # Script to initiate a PPP connection. This is the first part of the
  # pair of scripts. This is not a secure pair of scripts as the codes
  # are visible with the 'ps' command.  However, it is simple.
  #
  # These are the parameters. Change as needed.
  TELEPHONE=555-1212      # The telephone number for the connection
  ACCOUNT=george          # The account name for logon (as in 'George Burns')
  PASSWORD=gracie         # The password for this account (and 'Gracie Allen')
  LOCAL_IP=0.0.0.0        # Local IP address if known. Dynamic = 0.0.0.0
  REMOTE_IP=0.0.0.0       # Remote IP address if desired. Normally 0.0.0.0
  NETMASK=255.255.255.0   # The proper netmask if needed
  #
  # Export them so that they will be available to 'ppp-on-dialer'
  export TELEPHONE ACCOUNT PASSWORD
  #
  # This is the location of the script which dials the phone and logs
  # in.  Please use the absolute file name as the $PATH variable is not
  # used on the connect option.  (To do so on a 'root' account would be
  # a security hole so don't ask.)
  #
  DIALER_SCRIPT=/etc/ppp/ppp-on-dialer
  #
  # Initiate the connection
  #
  #
  exec /usr/sbin/pppd debug /dev/ttySx 38400 \
          $LOCAL_IP:$REMOTE_IP \
          connect $DIALER_SCRIPT
  ______________________________________________________________________

  Here is the ppp-on-dialer script:-

  ______________________________________________________________________
  #!/bin/sh
  #
  # This is part 2 of the ppp-on script. It will perform the connection
  # protocol for the desired connection.
  #
  /usr/sbin/chat -v                                                 \
          TIMEOUT         3                               \
          ABORT           '\nBUSY\r'                      \
          ABORT           '\nNO ANSWER\r'                 \
          ABORT           '\nRINGING\r\n\r\nRINGING\r'    \
          ''              \rAT                            \
          'OK-+++\c-OK'   ATH0                            \
          TIMEOUT         30                              \
          OK              ATDT$TELEPHONE                  \
          CONNECT         ''                              \
          ogin:--ogin:    $ACCOUNT                        \
          assword:        $PASSWORD
  ______________________________________________________________________

  For PPP-2.2, the ppp-off script looks like:-

  ______________________________________________________________________
  #!/bin/sh
  ######################################################################
  #
  # Determine the device to be terminated.
  #
  if [ "$1" = "" ]; then
          DEVICE=ppp0
  else
          DEVICE=$1
  fi

  ######################################################################
  #
  # If the ppp0 pid file is present then the program is running. Stop it.
  if [ -r /var/run/$DEVICE.pid ]; then
          kill -INT `cat /var/run/$DEVICE.pid`
  #
  # If the kill did not work then there is no process running for this
  # pid. It may also mean that the lock file will be left. You may wish
  # to delete the lock file at the same time.
          if [ ! "$?" = "0" ]; then
                  rm -f /var/run/$DEVICE.pid
                  echo "ERROR: Removed stale pid file"
                  exit 1
          fi
  #
  # Success. Let pppd clean up its own junk.
          echo "PPP link to $DEVICE terminated."
          exit 0
  fi
  #
  # The ppp process is not running for ppp0
  echo "ERROR: PPP link is not active on $DEVICE"
  exit 1
  ______________________________________________________________________

  15.3.  Editing the supplied PPP startup scripts

  As the new scripts come in two parts, we will edit them in turn.

  15.3.1.  The ppp-on script

  You will need to edit the script to reflect YOUR user name at your
  ISP, YOUR password at your ISP, the telephone number of your ISP.

  Each of the lines like TELEPHONE= actually set up shell variables that
  contain the information to the right of the '=' (excluding the
  comments of course). So edit each of these lines so it is correct for
  your ISP and connection.

  Also, as you are setting the IP number (if you need to) in the
  /etc/ppp/options file, DELETE the line that says

  ______________________________________________________________________
  $LOCAL_IP:$REMOTE_IP \
  ______________________________________________________________________

  Also, make sure that the shell variable DIALER_SCRIPT points at the
  full path and name of the dialer script that you are actually going to
  use. So, if you have moved this or renamed the script, make sure you
  edit this line correctly in the ppp-on script!

  15.3.2.  The ppp-on-dialer script

  This is the second of the scripts that actually brings up our ppp
  link.

  Note: a chat script is normally all on one line. the backslashes are
  used to allow line continuations across several physical lines (for
  human readability) and do not form part of the script itself.

  However, it is very useful to look at it in detail so that we
  understand what it is actually (supposed) to be doing!

  15.4.  What a Chat script means...

  A chat script is a sequence of "expect string" "send string" pairs. In
  particular, note that we ALWAYS expect something before we send
  something.

  If we are to send something WITHOUT receiving anything first, we must
  use an empty expect string (indicated by "") and similarly for
  expecting something without sending anything! Also, if a string
  consists of several words, (e.g. NO CARRIER), you must quote the
  string so that it is seen as a single entity by chat.

  The chat line in our template is:-

  ______________________________________________________________________
  exec /usr/sbin/chat -v
  ______________________________________________________________________

  Invoke chat, the -v tells chat to copy ALL its I/O into the system log
  (usually /var/log/messages). Once you are happy that the chat script
  is working reliably, edit this line to remove the -v to save
  unnecessary clutter in your syslog.

  ______________________________________________________________________
  TIMEOUT         3
  ______________________________________________________________________

  This sets the timeout for the receipt of expected input to three sec¡
  onds. You may need to increase this to say 5 or 10 seconds if you are
  using a really slow modem!

  ______________________________________________________________________
  ABORT           '\nBUSY\r'
  ______________________________________________________________________

  If the string BUSY is received, abort the operation.

  ______________________________________________________________________
  ABORT           '\nNO ANSWER\r'
  ______________________________________________________________________

  If the string NO ANSWER is received, abort the operation

  ______________________________________________________________________
  ABORT           '\nRINGING\r\n\r\nRINGING\r'
  ______________________________________________________________________

  If the (repeated) string RINGING is received, abort the operation.
  This is because someone is ringing your phone line!

  ______________________________________________________________________
  "              \rAT
  ______________________________________________________________________

  Expect nothing from the modem and send the string AT.

  ______________________________________________________________________
  OK-+++\c-OK   ATH0
  ______________________________________________________________________

  This one is a bit more complicated as it uses some of chat's error
  recovery capabilities.

  What is says is...Expect OK, if it is NOT received (because the modem
  is not in command mode) then send +++ (the standard Hayes-compatible
  modem string that returns the modem to command mode) and expect OK.
  Then send ATH0 (the modem hang up string). This allows your script to
  cope with the situation of your modem being stuck on-line!

  ______________________________________________________________________
  TIMEOUT         30
  ______________________________________________________________________

  Set the timeout to 30 seconds for the remainder of the script. If you
  experience trouble with the chat script aborting due to timeouts,
  increase this to 45 seconds or more.

  ______________________________________________________________________
  OK              ATDT$TELEPHONE
  ______________________________________________________________________

  Expect OK (the modem's response to the ATH0 command) and dial the
  number we want to call.

  ______________________________________________________________________
  CONNECT         ''
  ______________________________________________________________________

  Expect CONNECT (which our modem sends when the remote modem answers)
  and send nothing in reply.

  ______________________________________________________________________
  ogin:--ogin:    $ACCOUNT
  ______________________________________________________________________

  Again, we have some error recovery built in here. Expect the login
  prompt (...ogin:) but if we don't receive it by the timeout, send a
  return and then look for the login prompt again. When the prompt is
  received, send the username (stored in the shell variable $ACCOUNT).

  ______________________________________________________________________
  assword:        $PASSWORD
  ______________________________________________________________________

  Expect the password prompt and send our password (again, stored in a
  shell variable).

  This chat script has reasonable error recovery capability. Chat has
  considerably more features than demonstrated here. For more
  information consult the chat manual page (man 8 chat).

  15.4.1.  Starting PPP at the server end

  Whilst the ppp-on-dialer script is fine for servers that automatically
  start pppd at the server end once you have logged in, some servers
  require that you explicitly start PPP on the server.

  If you need to issue a command to start up PPP on the server, you DO
  need to edit the ppp-on-dialer script.

  At the END of the script (after the password line) add an additional
  expect send pair - this one would look for your login prompt (beware
  of characters that have a special meaning in the Bourne shell - such
  as $ and  or  (open and close square brackets).

  Once chat has found the shell prompt, chat must issue the ppp start up
  command required for your ISPs PPP server.

  In my case, my PPP server uses the standard Linux Bash prompt

  ______________________________________________________________________
  [hartr@kepler hartr]$
  ______________________________________________________________________

  and requires that I type

  ______________________________________________________________________
  ppp
  ______________________________________________________________________

  to start up PPP on the server.

  It is a good idea to allow for a bit of error recovery here, so in my
  case I use

  ______________________________________________________________________
          hartr--hartr    ppp
  ______________________________________________________________________

  This says,  if we don't receive the prompt within the timeout, send a
  carriage return and looks for the prompt again.

  Once the prompt is received, then send the string ppp.

  Note: don't forget to add a \ to the end of the previous line so chat
  still thinks the entire chat script is on one line!

  Unfortunately, some servers produce a very variable set of prompts!
  You may need to log in several times using minicom to understand what
  is going on and pick the stable "expect" strings.

  15.5.  A chat script for PAP/CHAP authenticated connections

  If your ISP is using PAP/CHAP, then your chat script is much simpler.
  All your chat script needs to do is dial the telephone, wait for a
  connect and then let pppd handle the logging in!

  ______________________________________________________________________
  #!/bin/sh
  #
  # This is part 2 of the ppp-on script. It will perform the connection
  # protocol for the desired connection.
  #
  exec /usr/sbin/chat -v                                  \
          TIMEOUT         3                               \
          ABORT           '\nBUSY\r'                      \
          ABORT           '\nNO ANSWER\r'                 \
          ABORT           '\nRINGING\r\n\r\nRINGING\r'    \
          ''              \rAT                            \
          'OK-+++\c-OK'   ATH0                            \
          TIMEOUT         30                              \
          OK              ATDT$TELEPHONE                  \
          CONNECT         ''                              \
  ______________________________________________________________________

  15.6.  The pppd debug and file option_file options

  As we have already seen, you can turn on debug information logging
  with the -d option to pppd. The 'debug' option is equivalent to this.

  As we are establishing a new connection with a new script, leave in
  the debug option for now. (Warning: if your disk space is tight,
  logging pppd exchanges can rapidly extend your syslog file and run you
  into trouble - but to do this you must fail to connect and keep on
  trying for quite a few minutes).

  Once you are happy that all is working properly, then you can remove
  this option.

  If you have called your ppp options file anything other than
  /etc/ppp/options or /etc/ppp/options.ttySx, specify the file name with
  the file option to pppd - e.g.

  ______________________________________________________________________
  exec /usr/sbin/pppd debug file options.myserver /dev/ttyS0 38400 \
  ______________________________________________________________________

  16.  Testing your connection script

  Open a new root Xterm (if you are in X) or open a new virtual console
  and log in as root.

  In this new session, issue the command

       tail -f /var/log/messages

  (or whatever your system log file is).

  In the first window (or virtual console) issue the command

       ppp-on &

  (or whatever name you have called your edited version of
  /usr/sbin/ppp- on). If you do not put the script into the background
  by specifying & at the end of the command, you will not get your
  terminal prompt back until ppp exits (when the link terminates).

  Now switch back to the window that is tracking your system log.

  You will see something like the following (provided you specified -v
  to chat and -d to pppd)....this is the chat script and responses being
  logged to the system log file followed by the start up information for
  pppd :-

  ______________________________________________________________________
  Oct 21 16:09:58 hwin chat[19868]: abort on (NO CARRIER)
  Oct 21 16:09:59 hwin chat[19868]: abort on (BUSY)
  Oct 21 16:09:59 hwin chat[19868]: send (ATZ^M)
  Oct 21 16:09:59 hwin chat[19868]: expect (OK)
  Oct 21 16:10:00 hwin chat[19868]: ATZ^M^M
  Oct 21 16:10:00 hwin chat[19868]: OK -- got it
  Oct 21 16:10:00 hwin chat[19868]: send (ATDT722298^M)
  Oct 21 16:10:00 hwin chat[19868]: expect (CONNECT)
  Oct 21 16:10:00 hwin chat[19868]: ^M
  Oct 21 16:10:22 hwin chat[19868]: ATDT722298^M^M
  Oct 21 16:10:22 hwin chat[19868]: CONNECT -- got it
  Oct 21 16:10:22 hwin chat[19868]: send (^M)
  Oct 21 16:10:22 hwin chat[19868]: expect (ogin:)
  Oct 21 16:10:23 hwin chat[19868]: kepler login: -- got it
  Oct 21 16:10:23 hwin chat[19868]: send (hartr^M)
  Oct 21 16:10:23 hwin chat[19868]: expect (ssword:)
  Oct 21 16:10:23 hwin chat[19868]:  hartr^M
  Oct 21 16:10:23 hwin chat[19868]: Password: -- got it
  Oct 21 16:10:23 hwin chat[19868]: send (??????^M)
  Oct 21 16:10:23 hwin chat[19868]: expect (hartr)
  Oct 21 16:10:24 hwin chat[19868]: [hartr -- got it
  Oct 21 16:10:24 hwin chat[19868]: send (ppp^M)
  Oct 21 16:10:27 hwin pppd[19872]: pppd 2.1.2 started by root, uid 0
  Oct 21 16:10:27 hwin pppd[19873]: Using interface ppp0
  Oct 21 16:10:27 hwin pppd[19873]: Connect: ppp0 <--> /dev/cua1
  Oct 21 16:10:27 hwin pppd[19873]: fsm_sdata(LCP): Sent code 1, id 1.
  Oct 21 16:10:27 hwin pppd[19873]: LCP: sending Configure-Request, id 1
  Oct 21 16:10:27 hwin pppd[19873]: fsm_rconfreq(LCP): Rcvd id 1.
  Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: rcvd MRU
  Oct 21 16:10:27 hwin pppd[19873]: (1500)
  Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
  Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: rcvd ASYNCMAP
  Oct 21 16:10:27 hwin pppd[19873]: (0)
  Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
  Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: rcvd MAGICNUMBER
  Oct 21 16:10:27 hwin pppd[19873]: (a098b898)
  Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
  Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: rcvd PCOMPRESSION
  Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
  Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: rcvd ACCOMPRESSION
  Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
  Oct 21 16:10:27 hwin pppd[19873]: lcp_reqci: returning CONFACK.
  Oct 21 16:10:27 hwin pppd[19873]: fsm_sdata(LCP): Sent code 2, id 1.
  Oct 21 16:10:27 hwin pppd[19873]: fsm_rconfack(LCP): Rcvd id 1.
  Oct 21 16:10:27 hwin pppd[19873]: fsm_sdata(IPCP): Sent code 1, id 1.
  Oct 21 16:10:27 hwin pppd[19873]: IPCP: sending Configure-Request, id 1
  Oct 21 16:10:27 hwin pppd[19873]: fsm_rconfreq(IPCP): Rcvd id 1.
  Oct 21 16:10:27 hwin pppd[19873]: ipcp: received ADDR
  Oct 21 16:10:27 hwin pppd[19873]: (10.144.153.51)
  Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
  Oct 21 16:10:27 hwin pppd[19873]: ipcp: received COMPRESSTYPE
  Oct 21 16:10:27 hwin pppd[19873]: (45)
  Oct 21 16:10:27 hwin pppd[19873]:  (ACK)
  Oct 21 16:10:27 hwin pppd[19873]: ipcp: returning Configure-ACK
  Oct 21 16:10:28 hwin pppd[19873]: fsm_sdata(IPCP): Sent code 2, id 1.
  Oct 21 16:10:30 hwin pppd[19873]: fsm_sdata(IPCP): Sent code 1, id 1.
  Oct 21 16:10:30 hwin pppd[19873]: IPCP: sending Configure-Request, id 1
  Oct 21 16:10:30 hwin pppd[19873]: fsm_rconfreq(IPCP): Rcvd id 255.
  Oct 21 16:10:31 hwin pppd[19873]: ipcp: received ADDR
  Oct 21 16:10:31 hwin pppd[19873]: (10.144.153.51)
  Oct 21 16:10:31 hwin pppd[19873]:  (ACK)
  Oct 21 16:10:31 hwin pppd[19873]: ipcp: received COMPRESSTYPE
  Oct 21 16:10:31 hwin pppd[19873]: (45)
  Oct 21 16:10:31 hwin pppd[19873]:  (ACK)
  Oct 21 16:10:31 hwin pppd[19873]: ipcp: returning Configure-ACK
  Oct 21 16:10:31 hwin pppd[19873]: fsm_sdata(IPCP): Sent code 2, id 255.
  Oct 21 16:10:31 hwin pppd[19873]: fsm_rconfack(IPCP): Rcvd id 1.
  Oct 21 16:10:31 hwin pppd[19873]: ipcp: up
  Oct 21 16:10:31 hwin pppd[19873]: local  IP address 10.144.153.104
  Oct 21 16:10:31 hwin pppd[19873]: remote IP address 10.144.153.51
  ______________________________________________________________________

  (Note - I am using STATIC IP numbers - hence my machine sent that to
  the PPP server - you won't see this if you are using DYNAMIC IP
  numbers.)  Also, this server requires a specific command to start ppp
  at its end.

  This looks OK - so test it out as before with pings to IP numbers and
  host names.

  Fire up you web browser or whatever and go surfing - you are
  connected!

  17.  Shutting down the PPP link

  When you have finished with the PPP link, use the standard ppp-off
  command to shut it down (remember - you need to be root or a member of
  the PPP group!).

  In your system log you will see something like:-

  ______________________________________________________________________
  Oct 21 16:10:45 hwin pppd[19873]: Interrupt received: terminating link
  Oct 21 16:10:45 hwin pppd[19873]: ipcp: down
  Oct 21 16:10:45 hwin pppd[19873]: default route ioctl(SIOCDELRT): Bad address
  Oct 21 16:10:45 hwin pppd[19873]: fsm_sdata(LCP): Sent code 5, id 2.
  Oct 21 16:10:46 hwin pppd[19873]: fsm_rtermack(LCP).
  Oct 21 16:10:46 hwin pppd[19873]: Connection terminated.
  Oct 21 16:10:46 hwin pppd[19873]: Exit.
  ______________________________________________________________________

  Don't worry about the SIOCDELRT - this is just pppd noting that it is
  terminating and is nothing to worry about.

  18.  Debugging

  There are any number of reasons that your connection does not work -
  chat has failed to complete correctly, you have a dirty line, etc. So
  check your syslog for indications.

  18.1.  I have compiled PPP support into the kernel, but...

  A very common problem is that people compile PPP support into the
  kernel and yet when they try to run pppd, the kernel complains that it
  does not support ppp! There are a variety of reasons this can occur.

  18.1.1.  Whilst you have recompiled your kernel to support ppp, you
  are not booting the new kernel. This can happen if you do not update
  /etc/lilo.conf and rerun lilo.  Are you booting the right kernel?

  A good check on the kernel can be obtained by issuing the command
  uname -a, which should produce a line like

  ______________________________________________________________________
  Linux archenland 2.0.28 #2 Thu Feb 13 12:31:37 EST 1997 i586
  ______________________________________________________________________

  This gives the kernel version and the date on which this kernel was
  compiled - which should give you a pretty good idea of what is going
  on.

  18.1.2.  Did you compile ppp kernel support as a module?

  If you compiled your kernel ppp support as a module, but did not make
  and install the modules, then you can get this error. Check the
  kernel-HOWTO and the README file in /usr/src/linux!

  Another module connected possibility is that you are expecting
  required modules to be automatically loaded, but are not running the
  kerneld daemon (which auto-loads and unloads modules on the fly).
  Check the kerneld mini-HOWTO for information on setting up kerneld.

  18.1.3.  Are you using the correct version of PPP for your kernel?

  You must use ppp-2.2 with kernel version 2.0.x. You can use ppp-2.2
  with kernel version 1.2.x (if you patch the kernel) otherwise you must
  use ppp-2.1.2.

  18.1.4.  Are you running pppd as root?

  If you are not running pppd as the root user (and pppd is not suid to
  root), you can receive this message.

  18.2.  My modem connects but ppp never starts up

  There are innumerable variations on this (take a look in
  comp.os.linux...).

  A VERY common mistake is that you have mistyped something in your
  scripts. The only thing to do here is to make sure you are logging the
  chat conversation between you Linux PC and the server into your syslog
  (/var/log/messages) and then go through this line by line to make.
  You may need to dial into the ppp server manually to check things out
  again.

  You need to check the log against the actual prompts very carefully -
  and bear in mind that we humans have a tendency to read what we THINK
  we have typed - not what is actually there!

  18.3.  The syslog says "serial line is not 8 bit clean..."

  There are variations on this too - such as serial line looped back
  etc., and the cause can be one (or a sequence) of a number of things.

  To understand what is going on here, it is necessary to grasp a bit of
  what is going on behind the scenes in pppd itself.

  When pppd starts up, it sends LCP (link control protocol) packets to
  the remote machine. If it receives a valid response it then goes on to
  the next stage (using IPCP - IP control protocol packets) and only
  when this negotiation completes is the actual IP layer started so that
  you can use the PPP link.

  If there is no ppp server operating at the remote end when your PC
  sends lcp packets, these get reflected by the login process at the far
  end. As these packets use 8 bits, reflecting them strips the 8th bit
  (remember, ASCII is a 7 bit code). PPP sees this and complains
  accordingly.

  There are several reasons this reflection can occur.

  18.3.1.  You are not correctly logging into the server

  When your chat script completes, pppd starts on your PC. However, if
  you have not completed the log in process to the server (including
  sending any command required to start PPP  on the server), PPP will
  not start.

  So, the lcp packets are reflected and you receive this error.

  You need to carefully check and correct (if necessary) your chat
  script (see above).

  18.3.2.  You are not starting PPP on the server

  Some PPP servers require you to enter a command and/or a RETURN after
  completing the log in process before the remote end starts ppp.

  Check your chat script (see above).

  If you log in manually and find you need to send a RETURN after this
  to start PPP, simply add a blank expect/send pair to the end of your
  chat script (an empty send string actually sends a RETURN).

  18.3.3.  The remote PPP process is slow to start

  This one is a bit tricksy!

  By default, your Linux pppd is compiled to send a maximum of 10 lcp
  configuration requests. If the server is a bit slow to start up, all
  10 such requests can be sent before the remote PPP is ready to receive
  them.

  On your machine, pppd sees all 10 requests reflected back (with the
  8th bit stripped) and exits.

  There are two ways round this:-

  Add lcp-max-configure 30 to your ppp options. This increases the
  maximum number of lcp configure packets pppd sends before giving up.
  For really slow server, you may need even more than this.

  Alternatively, you can get a bit tricksy in return. You may have
  noticed that when you logged in by hand to the PPP server and PPP
  started there, the first character of the ppp garbage that appears was
  always the tilde character (~).

  Using this knowledge we can add a new expect/send pair to the end of
  the chat script which expects a tilde and sends nothing. This would
  look like:-

  ______________________________________________________________________
  \~      ''
  ______________________________________________________________________

  Note: as the tilde character has a special meaning in the shell, it
  must be escaped (and hence the leading backslash).

  18.4.  Default route not set

  If pppd refuses to set up a default route, it is because (quite
  correctly) it refuses remove/replace an existing default route.

  The usual reason that this error occurs is that some distributions set
  up a default route via your Ethernet card as opposed to setting up a
  specific network route.

  See the Linux NAG and the Net2/3 HOWTOs for information on correctly
  setting up your Ethernet card and associated routes.

  An alternative to this is that your LAN uses a gateway/router already
  and your routing table has been set up to point the default route at
  this.

  Fixing up this last situation can require a fair bit of IP networking
  knowledge and is beyond the scope of this HOWTO. It is suggested you
  obtain some expert advice (via the news groups of from someone locally
  you can ask).

  18.5.  Other Problems

  There are many reasons apart from these that ppp fails to connect
  and/or operate properly.

  Look in the PPP FAQ (which is really a series of questions and
  answers). This is a very comprehensive document and the answers ARE
  there! From my own (sad) experience, if the answer to your problems is
  not there, the problem is NOT ppp's fault! In my case I was using an
  ELF kernel that I had not upgraded to  the appropriate kernel modules.
  I only wasted about 2 days (and most of one night) cursing what had
  been a perfect PPP server before the light dawned!

  19.  Getting Help when totally stuck

  If you can't get your PPP link to work, go back through this document
  and check everything - in conjunction with the output created by
  "chat-v..."  and "pppd -d" in you system log.

  Also consult the PPP documentation and FAQ plus the other documents
  mention herein!

  If you are still stuck, try the comp.os.linux.misc and
  comp.os.linux.networking newsgroups are reasonably regularly scanned
  by people that can help you with PPP as is comp.protocols.ppp

  You can try sending me personal email, but I do have a day job (and a
  life) and I do not guarantee to respond quickly (if at all) as this
  depends on my current work load and the state of my private life!

  In particular - DO NOT POST REAMS OF DEBUGGING OUTPUT TO THE NEWS
  GROUPS NOR SEND IT TO ME BY EMAIL - the former wastes huge amounts of
  network bandwidth and the latter will be consigned to /dev/null
  (unless I have specifically requested it).

  20.  Common Problems once the link is working

  One problem you will find is that many service providers will only
  support the connection software package that they distribute to new
  accounts. This is (typically) for Microsoft Windows :-( - and many
  service provider help desks seem to know nothing about Unix (or
  Linux). So, be prepared for limited assistance from them!

  You could of course do the individual a favour and educate then about
  Linux (any ISP help desk person should be reasonably 'with it' in
  Internet terms and that means they should have a home Linux box - of
  course it does)!

  20.1.  I can't see beyond the PPP server I connect to

  OK - your PPP connection is up and running and you can ping the PPP
  server by IP number (the second or "remote" IP number shown by
  ifconfig ppp0), but you can't reach anything beyond this.

  First of all, try pinging the IP numbers you have specified in
  /etc/resolv.conf as name servers. If this works, you can see beyond
  your PPP server (unless this has the same IP number as the "remote" IP
  number of your connection). So now try pinging the full Internet name
  of your service provider - eg

  ping my.provider.net.au

  If this does NOT work, you have a problem with the name resolution.
  This is probably because of a typo in your /etc/resolv.conf file.
  Check this carefully against the information you acquired by ringing
  your service provider. If all looks OK, ring your service provider and
  check that you wrote down the IP numbers correctly.

  If it STILL doesn't work (and your service provider confirms that his
  name servers are up and running), you have a problem somewhere else -
  and I suggest you check carefully through your Linux installation
  (looking particularly for file permissions).

  If you STILL can't ping your service provider's IP name servers by IP
  number, either they are down (give them a voice call and check) or
  there is a routing problem at your service provider's end. Again, ring
  them and check this out.

  One possibility is that the "remote end" is a Linux PPP server where
  the IP forwarding option has not been specified in the kernel!

  A good general test is to try connecting to your service provider
  using the software that most supply for (gulp) Microsoft Windows. If
  everything works from another operating system to exactly the same
  account, then the problem is with your Linux system and NOT your
  service provider.

  20.2.  I can send email, but not receive it

  If you are using dynamic IP numbers, this is perfectly normal. See
  "Setting up Services" below.

  20.3.  Why can't people finger, WWW, gopher, talk etc to my machine?

  Again, if you are using dynamic IP numbers, this is perfectly normal.
  See "Setting up Services" below.

  21.  Using Internet services with Dynamic IP numbers

  If you are using dynamic IP numbers (and many service providers will
  only give you a dynamic IP number unless you pay significantly more
  for your connection), then you have to recognise the limitations this
  imposes.

  First of all, outbound service requests will work just fine. That is,
  you can send email using sendmail (provided you have correctly set up
  sendmail), ftp files from remote sites, finger users on other
  machines, browse the web etc.

  In particular, you can answer email that you have brought down to your
  machine whilst you are off line. Mail will simply sit in your mail
  queue until you dial back into your ISP.
  However, your machine is NOT connected to the Internet 24 hours a day,
  nor does it have the same IP number every time it is connected. So it
  is impossible for you to receive email directed to your machine, and
  very difficult to set up a web or ftp server that your friends can
  access! As far as the Internet is concerned your machine does not
  exist as a unique, permanently contactable machine as it does not have
  a unique IP number (remember - other machines will be using the IP
  number when they are allocated it on dial in).

  If you set up a WWW (or any other server), it is totally unknown by
  any user on the Internet UNLESS they know that your machine is
  connected AND its actual (current) IP number. There are a number of
  ways they can get this info, ranging from you ringing them, sending
  them email to tell them or cunning use of ".plan" files on a shell
  account at your service provider (assuming that your provider allows
  shell and finger access).

  Now, for most users, this is not a problem - all that most people want
  is to send and receive email (using your account on your service
  provider) and make outbound connections to WWW, ftp and other servers
  on the Internet. If you MUST have inbound connections to your server,
  you should really get a static IP number. Alternatively you can
  explore the methods hinted at above...

  21.1.  Setting up email

  Even for dynamic IP numbers, you can certainly configure sendmail on
  your machine to send out any email that you compose locally.
  Configuration of sendmail can be obscure and difficult - so this
  document does not attempt to tell you how to do this. However, you
  should probably configure sendmail so that your Internet service
  provider is designated as your "smart relay" host (the sendmail.cf DS
  option). (For more sendmail configuration info, see the sendmail
  documents - and look at the m4 configurations that come with sendmail.
  There is almost certain to be one there that will meet your needs).

  There are also excellent books on Sendmail (notably the 'bible' from
  O'Reilly and Associates), but these are almost certainly overkill for
  most users!

  Once you have sendmail configured, you will probably want to have
  sendmail dispatch any messages that have been sitting in the outbound
  mail queue as soon as the PPP connection comes up. To do this, add the
  command

       sendmail -q &

  to your /etc/ppp/ip-up script (see below).

  Inbound email is a problem for dynamic IP numbers. The way to handle
  this is to:-

  ╖  configure your mail user agent so that all mail is sent out with a
     "reply to" header giving your email address at your Internet
     Service provider.
     If you can, you should also set your FROM address to be your email
     address at your ISP as well.

  ╖  use the popclient, fetchmail programs to retrieve your email from
     your service provider. Alternatively, if your ISP is using IMAP,
     use an IMAP enabled mail user agent (such as pine).

  You can automate this process at dial up time by putting the necessary
  commands in the /etc/ppp/ip-up script (see below).

  21.2.  Setting Up a local Name server

  Whilst you can quite happily use the domain name servers located at
  your ISP, you can also set up a local caching only (secondary) name
  server that is brought up by the ip-up script. The advantage of
  running a local (caching only) name server is that it will save you
  time (and bandwidth) if you frequently contact the same sites during a
  long on-line session.

  DNS configuration for a caching only nameserver (that uses a
  "forwarders' line in the named.boot file pointing at your ISPs DNS) is
  relatively simple. The O'Reilly book (DNS and Bind) explains all you
  want to know about this.

  There is also a DNS-HOWTO available.

  If you are running a small LAN that can access the Internet through
  you Linux PC (using IP Masquerade for example), it is probably a good
  idea to run a local name server (with a forwarders directive) whilst
  the link is up as this will minimise the bandwidth and delays
  associated with name resolution.

  One point of Nettiquette: ask permission from your ISP before you
  start using a secondary, caching only name server in your ISP's
  domain.  Properly configured, your DNS will not cause any problems to
  your ISP at all, but if you get things wrong, it can cause problems.

  22.  Linking two networks using PPP

  There is basically no difference between linking a single Linux PC to
  a PPP server and linking two LANs using PPP on a machine on each LAN.
  Remember, PPP is a peer to peer protocol.

  However, you DEFINITELY need to understand about how routing is
  established. Read the NET-2 howto and the Linux Network Administrator
  Guide (NAG). You will also find " TCP/IP Network Administration"
  (published by O'Reilly and Assoc - ISBN 0-937175-82-X) to be of
  invaluable assistance.

  If you are going to be sub networking an IP network number on either
  side of the link, you will also find the Linux (draft) sub networking
  mini-howto) to be of use. This is available at Linux Sub networking
  mini-HOWTO <http://www.interweft.com.au/other/>.

  In order to link two LANs, you must be using different IP network
  numbers (or subnets of the same network number) and you will need to
  use static IP numbers - or use IP masquerade. If you want to use IP
  masquerade, see the IP masquerade mini-howto for instructions on
  setting that up.

  22.1.  Setting up the IP numbers

  Arrange with the network administrator of the other LAN the IP numbers
  that will be used for each end of the PPP interface. If you are using
  static IP numbers, this will also probably require you to dial into a
  specific telephone number.

  Now edit the appropriate /etc/ppp/options[.ttyXX] file - it's a good
  idea to have a specific modem and port at your end for this
  connection. This may well require you to change your /etc/ppp/options
  file - and create appropriate options.ttyXX files for any other
  connections!

  Specify the IP numbers for your end of the PPP link in the appropriate
  options file exactly as shown above for static IP numbers.

  22.2.  Setting up the routing

  You must arrange that packets on your local LAN are routed across the
  interface that the PPP link establishes. This is a two stage process.

  First of all, you need to establish a route from the machine running
  the PPP link to the network(s) at the far end of the link. If the link
  is to the Internet, this can be handled by a default route established
  by pppd itself at your end of the connection using the 'defaultroute'
  option to pppd.

  If however, the link is only linking two LANs, then a specific network
  route must be added for each network that is accessible across the
  link.  This is done using a 'route' command for each network in the
  /etc/ppp/ip-up script (see After the link comes up...) for
  instructions on doing this.

  The second thing you need to do is to tell the other computers on your
  LAN that your Linux computer is actually the 'gateway' for the
  network(s) at the far end of the ppp link.

  Of course, the network administrator at the other end of the link has
  to do all this too! However, as s/he will be routing packets to your
  specific networks, a specific network route will be required, not a
  default route (unless the LANs at the far and of the link are linking
  into you to access the Internet across your connection).

  22.3.  Network security

  If you are linking you LAN to the Internet using PPP - or even just to
  a "foreign" LAN, you need to think about security issues. I strongly
  urge you to think about setting up a firewall!

  You should also speak to the LAN administrator at your site BEFORE you
  start linking to foreign LANs or the Internet this way. Failure to do
  so could earn you anything from no reaction to really serious trouble!

  23.  After the link comes up - the /etc/ppp/ip-up script

  Once the PPP link is established, pppd looks for /etc/ppp/ip-up. If
  this script exists and is executable, the PPP daemon executes the
  script. This allows you to automate any special routing commands that
  may be necessary and any other actions that you want to occur every
  time the PPP link is activated.

  This is just a shell script and can do anything that a shell script
  can do (i.e. virtually anything you want).

  For example, you can get sendmail to dispatch any waiting outbound
  messages in the mail queue.

  Similarly, you can insert the commands into ip-up to collect (using
  pop) any email waiting for you at your ISP.

  There are restrictions on /etc/ppp/ip-up:-

  ╖  It runs in a deliberately restricted environment to enhance
     security. This means you must give a full path to binaries etc.

  ╖  Technically, /etc/ppp/ip-up is a program not a script. This means
     it can be directly executed - and hence it requires the standard
     file magic (#!/bin/bash) at the start of the first line and must be
     readable and executable by root.

  23.1.  Special routing

  If you are linking two LANs, you will need to set up specific routes
  to the 'foreign' LANs. This is easily done using the /etc/ppp/ip-up
  script. The only difficulty arises if your machine handles multiple
  PPP links.

  This is because the /etc/ppp/ip-up is executed for EVERY ppp
  connection that comes up, so you need to carefully execute the correct
  routing commands for the particular link that comes up - and not when
  any other link comes up!

  23.2.  Handling email queues

  When the link between two LANs comes up, you may well want to make
  sure that email that is queued at either end is flushed - sent out to
  its destination. This is done by adding the appropriate sendmail
  invocation.

  Using the bash 'case' statement on an appropriate parameter that pppd
  passes into the script accomplishes this. For example, this is the
  /etc/ppp/ip-up script I use to handle our WAN links and the link to my
  home Ethernet (also handled on the same ppp server).

  23.3.  A sample /etc/ppp/ip-up script

  The example below provides a variety of example uses.

  ______________________________________________________________________
  #!/bin/bash
  #
  # Script which handles the routing issues as necessary for pppd
  # Only the link to Newman requires this handling.
  #
  # When the ppp link comes up, this script is called with the following
  # parameters
  #       $1      the interface name used by pppd (e.g. ppp3)
  #       $2      the tty device name
  #       $3      the tty device speed
  #       $4      the local IP address for the interface
  #       $5      the remote IP address
  #       $6      the parameter specified by the 'ipparam' option to pppd
  #
  case "$5" in
  # Handle the routing to the Newman Campus server
          202.12.126.1)
                  /sbin/route add -net 202.12.126.0 gw 202.12.126.1
  # and flush the mail queue to get their email there asap!
                  /usr/sbin/sendmail -q &
                  ;;
          139.130.177.2)
  # Our Internet link
  # When the link comes up, start the time server and synchronise to the world
  # provided it is not already running
                  if [ ! -f /var/lock/subsys/xntpd ]; then
                          /etc/rc.d/init.d/xntpd.init start &
                  fi
  # Start the news server (if not already running)
                  if [ ! -f /var/lock/subsys/news ]; then
                          /etc/rc.d/init.d/news start &
                  fi
                  ;;
          203.18.8.104)
  # Get the email down to my home machine as soon as the link comes up
  # No routing is required as my home Ethernet is handled by IP
  # masquerade and proxyarp routing.
                  /usr/sbin/sendmail -q &
                  ;;
          *)
  esac
  exit 0
  ______________________________________________________________________

  As a result of bringing up the ppp link to our Newman campus and this
  script, we end up with the following routing table entries (this
  machine also is our general dial up PPP server AND handles our
  Internet link). I have interspersed comments in the output to help
  explain what each entry is) :-

  ______________________________________________________________________
  [root@kepler /root]# route -n
  Kernel routing table
  Destination     Gateway         Genmask         Flags MSS    Window Use Iface
  # the HOST route to our remote internet gateway
  139.130.177.2   *               255.255.255.255 UH    1500   0      134 ppp4
  # the HOST route to our Newman campus server
  202.12.126.1    *               255.255.255.255 UH    1500   0       82 ppp5
  # the HOST route to my home ethernet
  203.18.8.104    *               255.255.255.255 UH    1500   0       74 ppp3
  # two of our general dial up PPP lines
  203.18.8.64     *               255.255.255.255 UH    552    0        0 ppp2
  203.18.8.62     *               255.255.255.255 UH    552    0        1 ppp1
  # the specific network route to the Newman campus LAN
  202.12.126.0    202.12.126.1    255.255.255.0   UG    1500   0        0 ppp5
  # the route to our local Ethernet (super-netting two adjacent C classes)
  203.18.8.0      *               255.255.254.0   U     1500   0     1683 eth0
  # the route to the loop back device
  127.0.0.0       *               255.0.0.0       U     3584   0      483 lo
  # the default route to the Internet
  default         139.130.177.2   *               UG    1500   0     3633 ppp4
  ______________________________________________________________________

  23.4.  Handling email

  The previous section shows how to handle the outgoing mail - simply by
  flushing the mail queue once the link is up.

  If you are running a WAN link, you can arrange with the network
  administrator of the remote LAN to do exactly the same thing. For
  example, at the Newman Campus end of our WAN link, the /etc/ppp/ip-up
  script looks like :-

  ______________________________________________________________________
  #!/bin/bash
  #
  # Script which handles the routing issues as necessary for pppd
  # Only the link to Hedland requires this handling.
  #
  # When the ppp link comes up, this script is called with the following
  # parameters
  #       $1      the interface name used by pppd (e.g. ppp3)
  #       $2      the tty device name
  #       $3      the tty device speed
  #       $4      the local IP address for the interface
  #       $5      the remote IP address
  #       $6      the parameter specified by the 'ipparam' option to pppd
  #
  case "$5" in
          203.18.8.4)
                  /usr/sbin/sendmail -q
                  ;;
          *)
  esac
  exit 0
  ______________________________________________________________________

  If however you have only a dynamic IP PPP link to your ISP, you need
  to get your email from the account on your ISPs machine. This is
  usually done using the POP (Post Office Protocol). This process can be
  handled using the 'popclient' program - and the ip-up script can
  automate this process for you too!

  Simply create a /etc/ppp/ip-up script that contains the appropriate
  invocation of popclient. For my laptop that runs Red Hat Linux (which
  I take on any travels), this is

  ______________________________________________________________________
  popclient -3 -c -u hartr -p <password> kepler.hedland.edu.au |formail -s procmail
  ______________________________________________________________________

  You could use slurp or whatever to do the same for news, and so forth.
  Remember, the ip-up script is just a standard bash script and so can
  be used to automate ANY function that needs to be accomplished every
  time the appropriate PPP link comes up.

  24.  Using /etc/ppp/ip-down

  You can create a script  that will be executed once the link has been
  terminated. This is stored in /etc/ppp/ip-down. It can be used to undo
  anything special that you did in the corresponding /etc/ppp/ip-up
  script.

  25.  Routing issues on a LAN

  If you are connected to a LAN but still want to use PPP on your
  personal Linux machine , you need to address some issues of the routes
  packets need to take from your machine to reach your LAN (through your
  Ethernet interface) and also to the remote PPP server and beyond.

  This section does NOT attempt to teach you about routing - it deals
  only with a simple, special case of (static) routing!

  I strongly urge you to read the Linux Network Administrator Guide
  (NAG) if you are NOT familiar with routing. Also the O'Reilly book
  "TCP/IP Network Administration" covers this topic in a very
  understandable form.

  The basic rule of static routing is that the DEFAULT route should be
  the one that points to the MOST number of network addresses. For other
  networks, enter specific routes to the routing table.

  The ONLY situation I am going to cover here is where your Linux box is
  on a LAN that is not connected to the Internet - and you want to dial
  out to the Internet for personal use whilst still connected to the
  LAN.

  First of all, make sure that your Ethernet route is set up to the
  specific network addresses available across your LAN - NOT set to the
  default route!

  Check this by issuing a route command, you should see something like
  the following:-

       [root@hwin /root]# route -n
       Kernel routing table
       Destination     Gateway         Genmask         Flags MSS    Window Use Iface
       loopback        *               255.255.255.0   U     1936   0       50 lo
       10.0.0.0        *               255.255.255.0   U     1436   0      565 eth0

  If your Ethernet interface (eth0) is pointing at the default route,
  (the first column will show "default" in the eth0 line) you need to
  change your Ethernet initialisation scripts to make it point at the
  specific network numbers rather than the default route (consult the
  Net2 HOWTO and NAG).

  This will allow pppd to set up your default route as shown below:-

       [root@hwin /root]# route -n
       Kernel routing table

       Destination     Gateway         Genmask         Flags MSS    Window Use Iface
       10.144.153.51   *               255.255.255.255 UH    488    0        0 ppp0
       127.0.0.0       *               255.255.255.0   U     1936   0       50 lo
       10.1.0.0        *               255.255.255.0   U     1436   0      569 eth0
       default         10.144.153.51   *               UG    488    0        3 ppp0

  As you can see, we have a host route to the PPP server (
  10.144.153.51) via ppp0 and also a default network route that uses the
  PPP server as its gateway.

  If your set up needs to be more complex than this - read the routing
  documents already mentioned and consult an expert at your site!

  If your LAN already has routers on it, you will already have gateways
  established to the wider networks available at your site. You should
  STILL point your default route at the PPP interface - and make the
  other routes specific to the networks they serve.

  25.1.  Note on Security

  When you set up a Linux box on an existing LAN to link into the
  Internet, you are potentially opening your entire LAN to the Internet
  - and the hackers that reside there. Before you do this, I strongly
  urge you to consult your network administrator and site security
  policy. If your PPP connection to the Internet is used to successfully
  attack your site, you will at the very least earn the intense anger of
  your fellow users, network and system administrators. You may also
  find yourself in very much more serious trouble!

  Before you connect a LAN to the Internet, you should consider the
  security implications of even a DYNAMIC connection - hence the earlier
  reference to the O'Reilly "Building Internet Firewalls"!

  26.  Setting up a PPP server

  As already mentioned, there are many ways to do this. What I present
  here is the way I do it (using a Cyclades multi-port serial card) and
  a rotary dial in set of telephone lines.

  If you don't like the method I present here, please feel free to go
  your own way. I would however, be pleased to include additional
  methods in future versions of the HOWTO. So, please send me your
  comments and methods!

  Please note, this section only concerns setting up Linux as a PPP
  server. I do not (ever) intend to include information on setting up
  special terminal servers and such.

  Also, I have yet to experiment with shadow passwords (but will be
  doing so sometime). Information currently presented does NOT therefore
  include any bells and whistles that are required by the shadow suite.

  26.1.  Kernel compilation

  All the earlier comments regarding kernel compilation and kernel
  versions versus pppd versions apply. This section assumes that you
  have read the earlier sections of this document!

  For a PPP server, you MUST include IP forwarding in your kernel.  You
  may also wish to include other capabilities (such as IP fire walls,
  accounting etc etc).

  If you are using a multi-port serial card, then you must obviously
  include the necessary drivers in your kernel too!

  26.2.  Overview of the server system

  We offer dial up PPP (and SLIP) accounts and shell accounts using the
  same user name/password pair. This has the advantages (for us) that a
  user requires only one account and can use it for all types of
  connectivity.

  As we are an educational organisation, we do not charge our staff and
  students for access, and so do not have to worry about accounting and
  charging issues.

  We operate a firewall between our site and the Internet, and this
  restricts some user access as the dial up lines are inside our
  (Internet) firewall (for fairly obvious reasons, details of our other
  internal fire walls are not presented here and are irrelevant in any
  case).

  The process a user goes through to establish a PPP link to our site
  (once they have a valid account of course) is :-
  ╖  Dial into our rotary dialer (this is a single phone number that
     connects to a bank of modems - the first free modem is then used).

  ╖  Log in using a valid user name and password pair.

  ╖  At the shell prompt, issue the command ppp to start PPP on the
     server.

  ╖  Start PPP on their PC (be it running Windows, DOS, Linux MAC OS or
     whatever - that is their problem).

  The server uses individual /etc/ppp/options.ttyXX files for each dial
  in port that set the remote IP number for dynamic IP allocation.  The
  server users proxyarp routing for the remote clients (set via the
  appropriate option to pppd). This obviates the need for routed or
  gated.

  When the user hangs up at their end, pppd detects this and tells the
  modem to hang up, bringing down the PPP link at the same time.

  26.3.  Getting the software together

  You will need the following software:-

  ╖  Linux, properly compiled to include the necessary options.

  ╖  The appropriate version of pppd for your kernel.

  ╖  A 'getty' program that intelligently handles modem communications.
     We use getty_ps2.0.7h, but mgetty is highly thought of. I
     understand that mgetty can detect a call that is using pap/chap
     (pap is the standard for Windows95) and invoke pppd automatically,
     but I have yet to explore this.

  ╖  An operational domain name server (DNS) that is accessible to your
     dial up users.
     You should really be running your own DNS if possible...

  26.4.  Setting up standard (shell access) dialup.

  Before you can set up your PPP server, your Linux box must be capable
  of handling standard dial up access.

  This howto does NOT cover setting this up. Please see the
  documentation of the getty of your choice and serial HOWTO for
  information on this.

  26.5.  Setting up the PPP options files

  You will need to set up the overall /etc/ppp/options with the common
  options for all dial up ports. The options we use are:-

  ______________________________________________________________________
  asyncmap 0
  netmask 255.255.254.0
  proxyarp
  lock
  crtscts
  modem
  ______________________________________________________________________

  Note - we do NOT use any (obvious) routing - and in particular there
  is no defaultroute option. The reason for this is that all you (as a
  PPP server) are required to do is to route packets from the ppp client
  out across your LAN/Internet and route packets to the client from your
  LAN and beyond.

  All that is necessary for this is a host route to the client machine
  and the use of the 'proxyarp' option to pppd.

  The 'proxyarp' option sets up (surprise) a proxy ARP entry in the PPP
  server's ARP table that basically says 'send all packets destined for
  the PPP client to me'. This is the easiest way to set up routing to a
  single PPP client - but you cannot use this if you are routing between
  two LANs - you must add proper network routes which can't use proxy
  ARP.

  You will almost certainly wish to provide dynamic IP number allocation
  to your dial up users. You can accomplish this by allocating an IP
  number to each dial up port. Now, create a /etc/ppp/options.ttyXX for
  each dial up port.

  In this, simply put the local (server) IP number and the IP number
  that is to be used for that port. For example

  ______________________________________________________________________
  kepler:slip01
  ______________________________________________________________________

  In particular, note that you can use valid host names in this file (I
  find that I only remember the IP numbers of critical machines and
  devices on my networks - names are more meaningful)!

  26.6.  Setting pppd up to allow users to (successfully) run it

  As starting a ppp link implies configuring a kernel device (a network
  interface) and manipulating the kernel routing tables, special
  privileges are required - in fact full root privileges.

  Fortunately, pppd has been designed to be 'safe' to run set uid to
  root.  So you will need to

  ______________________________________________________________________
  chmod u+s /usr/sbin/pppd
  ______________________________________________________________________

  When you list the file, it should then appear as

  ______________________________________________________________________
  -rwsr-xr-x   1 root     root        74224 Apr 28 07:17 /usr/sbin/pppd
  ______________________________________________________________________

  If you do not do this, users will be unable to set up their ppp link.

  26.7.  Setting up the global alias for pppd

  In order to simplify things for our dial up PPP users, we create a
  global alias (in /etc/bashrc) so that one simple command will start
  ppp on the server once they are logged in.

  This looks like

  ______________________________________________________________________
  alias ppp="exec /usr/sbin/pppd -detach"
  ______________________________________________________________________

  What this does is

  ╖  exec : this means replace the running program (in this case the
     shell) with the program that is run.

  ╖  pppd -detach : start up pppd and do NOT fork into the background.
     This ensures that when pppd exits there is no process hanging
     around.

  When a user logs in like this, they will appear in the output of 'w'
  as

  ______________________________________________________________________
    6:24pm  up 3 days,  7:00,  4 users,  load average: 0.05, 0.03, 0.00
  User     tty       login@  idle   JCPU   PCPU  what
  hartr    ttyC0     3:05am  9:14                -
  ______________________________________________________________________

  And that is it...I told you this was a simple, basic PPP server
  system!

  27.  Using PPP across a null modem (direct serial) connection

  This is very simple - there is no modem in the way so things are much
  simpler.

  First of all, choose one of the machines as a 'server', setting up a
  getty on the serial port so you can test that you do have connectivity
  using minicom to access the serial port on the 'client'.

  Once you have this functioning, you can remove the getty UNLESS you
  want to make sure that the connection is validated using user
  name/password pairs as for a dial up connection. As you have 'physical
  control' of both machines, I will presume that you do NOT want to do
  this.

  Now, on the server, remove the getty and make sure that you have the
  serial ports on both machines configured correctly using 'setserial'.

  All you need to do now is to start pppd on both systems. I will assume
  that the connection uses /dev/ttyS34 on both machines. So, on both
  machines execute the command:-

  ______________________________________________________________________
  pppd -detach crtscts lock <local IP>:<remote IP> /dev/ttyS3 38400 &
  ______________________________________________________________________

  This will bring up the link - but as yet you have no routing
  specified.  You can test the link by pinging to and fro to each
  machine. If this works, bring down the link by killing one of the pppd
  processes.

  The routing you need will of course depend on exactly what you are
  trying to do. Generally, one of the machines will be connected to an
  Ethernet (and beyond) and so the routing required is exactly the same
  as for a PPP server and client.

  So on the Ethernet equipped machine, the pppd command would be

  ______________________________________________________________________
  pppd -detach crtscts lock proxyarp <local IP>:<remote IP> /dev/ttyS3 38400 &
  ______________________________________________________________________

  and on the other machine

  ______________________________________________________________________
  pppd -detach crtscts lock defaultroute <local IP>:<remote IP> /dev/ttyS3 38400 &
  ______________________________________________________________________

  If you are linking two networks (using a serial link!) or have more
  complex routing requirements, you can use /etc/ppp/ip-up in exactly
  the same way as mentioned earlier in this document.

  Robert Hart
  Port Hedland, Western Australia
  Melbourne, Victoria, Australia August/October 1996 January/March 1997