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- ADSL HOWTO for Linux Systems
- David Fannin, dfannin@sushisoft.com
- v0.92, 10 April 1999
-
- How to setup a Linux System to work with Asymmetric Digital Subscriber
- Loop (ADSL), a new high-speed digital access line technology available
- from Telcos. ADSL is one of a family of digital subscriber line (DSL)
- technologies available to residential and business customers using
- existing copper loops, providing speeds from 384kbps to 1.5Mbps. This
- document provides an introduction to ADSL, and information on how to
- install, configuration and turn up service.
- ______________________________________________________________________
-
- Table of Contents
-
-
- 1. Legal Stuff
-
- 2. Introduction
-
- 3. ADSL Overview
-
- 3.1 What is ADSL?
- 3.2 ADSL Applications
- 3.3 What is xDSL/DSL?
- 3.4 Why so many speeds?
-
- 4. How it works.
-
- 4.1 CPE: ADSL ANT and NIC
- 4.2 Splitter or Splitterless Design
- 4.3 DSLAM
- 4.4 ISP connection
-
- 5. Ordering Service
-
- 5.1 Home Requirements
- 5.2 Telco Options
- 5.3 ISP Options
-
- 6. Wiring it up
-
- 6.1 Wire the Splitter/NID (at the SNI)
- 6.2 Wire the DSL Jack (at the computer location)
- 6.3 Install the ANT (at the computer location)
-
- 7. Configuring Linux
-
- 7.1 Install and Connect the NIC card
- 7.2 Configure the Ethernet Interface
- 7.3 Setting up a Router
- 7.4 Setting up a Firewall/Masquerading
-
- 8. Appendix
-
- 8.1 FAQs
- 8.2 Links
- 8.3 Credits
- 8.4 Glossary
-
-
- ______________________________________________________________________
-
-
-
-
- 1. Legal Stuff
-
- ADSL HOWTO for Linux Systems
-
- Copyright (C)1998,1999 David Fannin.
-
- This document is free; you can redistribute it and/or modify it under
- the terms of the GNU General Public License as published by the Free
- Software Foundation; either version 2 of the License, or (at your
- option) any later version.
-
- This document is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- General Public License for more details.
-
- You can get a copy of the GNU GPL at at
- <http://www.gnu.org/copyleft/gpl.html>.
-
-
- 2. Introduction
-
- This document addresses the ordering, installation and configuration
- of ADSL service for use on Linux Systems.
-
-
- ADSL or Asymmetric Digital Subscriber Loop is a high-speed Internet
- access technology that uses a commonly available telephone copper loop
- (same wire as your phone service). Designed to run on up to 80% of
- the telephone available in the United States, and utilizing line-
- adaptive modulation, ADSL provides data speeds from 384kbps to 1.5
- Mbps, normally using different speeds for the upstream and downstream
- channel (hence the " Asymmetric" ). ADSL provides a direct, dedicated
- pipe to an ISP.
-
-
- ADSL was designed for SOHO applications, such as a small business with
- 5-30 systems, or the high-end Linux user that has wants bandwidth and
- has some money to spend. Applications range from low-bandwidth
- server interconnection to streaming video applications. ADSL is
- designed and priced somewhere in between ISDN and T1 service,
- providing near T1 speeds without the cost/complexity/availability
- issues of T1. Since ADSL is a dedicated service, it avoids the delays
- and use charges inherent in ISDN service.
-
- This HOW-TO starts with a description of ADSL services and it many
- variants, and a block diagram of the components that make up the
- service. Next, a list of requirements for ordering ADSL are provided.
- Also included is guide on ADSL wiring and configuring your Linux
- System. I have also included an Appendix with a FAQ, a listing of
- interesting Links,and a Glossary.
-
- I welcome any and all comments on this document; They can be sent to
- dfannin@dnai.com .
-
- The latest version of this FAQ is available from
- <http://www.sushisoft.com/adsl/>.
-
-
- 3. ADSL Overview
-
-
- 3.1. What is ADSL?
-
- Asymmetric Digital Subscriber Line (ADSL) is:
-
- ╖ A Telephone Loop Technology that uses existing phone lines
-
- ╖ Provides high-speed data and analog voice (Data over Voice)
-
- ╖ Dedicated digital line for an IP connection
-
- ╖ Data rates (North America) combinations of :
- Upstream/downstream
- 256 kbps/256 kbps
- 384 kbps/128 kbps
- 384 kbps/384 kbps
- 384 kbps/1.5 Mbps
- and many others
-
- ╖ Wide range of CPE options, including Ethernet 10baseT Interfaces.
-
- ╖ Dedicated ISP connection (static or dynamic addresses)
-
- ╖ Can support an IP subnet (from 1 to 254 IP addresses, depending on
- ISP)
-
- ╖ Priced lower than dedicated private line (T1) connections
-
-
-
- 3.2. ADSL Applications
-
- ADSL was designed to provide a dedicated, high-speed data connection
- for Internet/Intranet Access, using existing copper phone lines. This
- allows ADSL to work on over 60-80% of the phone lines existing in the
- U.S. without modification. Additionally, ADSL provides speeds
- approaching T1 (1.5Mbps), which are much greater than analog modems
- (56kbps) or ISDN (128kbps) services provided over the same type of
- line. ADSL is usually priced to be much less other dedicated digital
- services, and is expected to priced somewhere between T1 and ISDN
- services (including the ISDN usage charges).
-
- The Telcos see ADSL as a competitive offering to the Cable Company's
- Cable Modems, and as such, are expected to provide competitive
- pricing/configuration offerings. Although Cable Modems are
- advertised as having 10-30Mbps bandwidth, they use a shared
- transmission medium with many other users on the same line, and
- therefore performance varies, perhaps greatly, with the amount of
- traffic and other users.
-
-
- ADSL is positioned for Home and Small Office (SOHO) applications that
- require high-speed Internet Access. Since it also provides dedicated
- access, It can be used for interconnecting low-bandwidth servers to
- the Internet, and would provide a great access solution for 5-20 PCs
- in an Office location. It is also a great solution for those Linux
- power users that just want high speed access from home:-).
-
-
- 3.3. What is xDSL/DSL?
-
- Digital Subscriber Line (DSL) provides a dedicated digital circuit
- from your home to the Telcos central office, using analog telephone
- line. DSL also provides a separate channel for voice phone
- conversations, which means analog calls (voice, fax. etc.) can be
- carried at the same time high-speed data is flowing across the line.
- DSL uses the frequency spectrum between 0kHz-4kHz for Analog Voice,
- and 4kHz-2.2MHz for data. xDSL is a generic acronym for a family of
- dedicated services, where the " x"stands for:
-
-
- ╖ ADSL Asymmetric Digital Subscriber Line: 1.5
- Mbps-384kbps/384-128kbps
-
- ╖ HDSL High-bit-rate Digital Subscriber Line: 1.5 Mbps/1.5 Mbps
- (4Wire)
-
- ╖ SDSL Single-line Digital Subscriber Line: 1.5 Mbps/1.5 Mbps
- (2Wire)
-
- ╖ VDSL Very high Digital Subscriber Line: 13 Mbps-52 Mbps/1.5
- Mbps- 2.3 Mbps.
-
- ╖ IDSL ISDN Digital Subscriber Line: 128 Kbps/128 Kbps.
-
- ╖ RADSL Rate Adaptive Digital Subscriber Line: 384kbps/128kbps
-
- ╖ UDSL Universal Digital Subscriber Line:
- 1.0Mbps-384kbps/384kbps-128kbps
- also called " splitterless" DSL or DSL-Lite, as it doesn't require
- a splitter.
-
- where Xbps/Ybps is X=Downstream Bit rate, Y=Upstream Bit rate
-
- 3.4. Why so many speeds?
-
- ADSL has to work over existing phone lines, which were designed 100
- years ago, and were never designed for digital services (See the FAQ
- answers for more information). Also, ADSL is a new service, and all
- the providers are trying to find the right price/feature combinations
- that will make it in the market.
-
- For the average user, the basic way of thinking about it is to segment
- the options into three categories:
-
- ╖ Low End Residential
-
- Speed ranges from 384kbps-128kbps, Asymmetric
-
-
- ╖ High End Residential or Business End User
-
- Speed ranges from 1.5Mbps-384kbps, Asymmetric
-
-
- ╖ High End Server
-
- Speed ranges from +2.0Mbps-1.1kbps, Symmetric
-
-
-
- 4. How it works.
-
- ADSL is made up of several parts (shown by Figures 1 and 2):
-
-
- ╖ ADSL Network Termination (ANT) and Network Interface Card (NIC)
-
- ╖ Splitter or Splitterless Design
-
- ╖ DSLAM and Telco Loop
-
- ╖ ISP connection
-
-
-
-
- Figure 1: ADSL Block Diagram (POTS Splitter)
-
-
- <-------Home/Office---------------> <-----Telco Central Office---->
- NID
- ----- -----
- 2 wire X-----------Voice-=| S | | D |
- phone | P | | S |=----- Voice Switch
- line | L | 2 wire | L |
- | I |=-------------=| A |
- | T | Local Loop | M |=----- ISP Connection
- 10baseT ---------- Data | T | | |
- Ethernet X--=| |=----=| E | -----
- or ---------- | R |
- ATMF ADSL -----
- NIC ANT
-
-
-
-
- 4.1. CPE: ADSL ANT and NIC
-
- The Customer Premises Equipment (CPE) for ADSL consists of the ANT
- and/or NIC card. The ADSL Network Termination (ANT), shown in Figure
- 1, is located at your home or office, provides an IP connection. ANTs
- come in several types:
-
- ╖ Router ANT with 10/100baseT Interface
-
- ╖ Bridge ANT with 10/100baseT Interface
-
- ╖ ANT with ATMF Interface
-
- ╖ ANT with USB Interface
-
- ╖ Integrated ANT/NIC Card
-
- In each case, the ANT/NIC provides the a router address to an ISP.
- Each Telco will specify the configurations that they will allow. The
- most desirable configuration for the Linux user is the ANT with a
- 10baseT Interface, since the cost/setup is the easiest. The other
- options require special drivers, which have, to date, not been made
- available for Linux. The bad news is that some providers allow only
- integrated ANT/NIC PCI cards that do not have Linux Drivers.
-
- Warning! Make sure any third party ANT/NIC you may purchase are
- compatible with your Telco provider. There are two major line
- encodings for ADSL (CAP, DMT), and several options for IP
- encapsulation. Your Telco should provide you a list of allowable
- options.
-
- The ANT is connected to your house's inside wire (2 wire phone line).
- This inside wire is connected to the data side of a POTS splitter, or,
- in the case of the splitterless version, directly connected to the
- local loop. Figure 1 shows the POTS splitter wiring, and Figure 2
- shows a splitterless type.
-
- In my case, I was provided with an Alcatel ANT, which supports a
- 10baseT (wired as a Crossover) RJ45 jack. I understand that a NIC card
- that fits directly in the PC will be available sometime in the future.
-
-
-
-
-
-
- Figure 2: ADSL Block Diagram (Splitterless Design)
-
-
- <-------Home/Office---------------> <-----Telco Central Office---->
- SNI
- - -----
- 2 wire X-[RJ11]---Voice----| | D |
- phone Filter | | S |=----- Voice Switch
- line | 2 wire | L |
- |=-------------=| A |
- | Local Loop | M |=----- ISP Connection
- 10baseT ---------- Data | | |
- Ethernet X--=| |=-----| -----
- or ----------
- ATMF ADSL
- NIC ANT
-
-
-
- 4.2. Splitter or Splitterless Design
-
- Somehow, the digital and analog signals need to be separated for all
- of this to work. Thus, a filter needs to be placed in the signal path
- at some point. There are two methods for doing this: Using a POTS
- Splitter or using RJ11 phone jack filters.
-
- First, in the POTS splitter method, device is located on the "side of
- the house" where the Telco line is connected. The splitter provides
- two functions. First, it is the "demarcation point" that separates the
- Telco wiring from the inside wiring. Second, it "splits" the DSL
- signal from Telco into a separated data channel and a voice channel.
- The voice channel is a normal analog phone line (2 wire), and the data
- channel is sent to the ANT. The splitter is a passive, non-powered
- device, which will allow the voice channel to operate even if the
- power fails at the home location. The Telco signal is sent to the
- splitter using an existing 2 wire line to the home. The Splitter is
- housed in the Network Interface Device (NID) on the outside of your
- house.
-
- Second, in the splitterless design, shown in Figure 2, the outside
- local loop is connected directly to the inside wire at the Subscriber
- Network Interface (SNI), the same box that is used today at your
- house. At each extension jack where you wish to plug in an analog
- phone, you place a special jack that contains a filter that removes
- the digital signal. This is called an RJ11 filter (RJ11 is the
- official Telco term used for your 4/6 pin phone jack). The extension
- used for your ANT does NOT use a filter (otherwise it won't work).
- That's all there is to it! It should also be noted that some low
- speed ADSLs will not require RJ-11 filters.
-
- The splitterless design is very desirable from the Telco point of
- view, as they won't have to roll any trucks to do the install work,
- and allows them to offer ADSL at a lower price. For most users, it
- doesn't really matter, in fact, the analog phones will still work
- without the RJ11 filter in place. The only thing is that you will hear
- a bit of a high pitched whine when you use the phone. However, this
- is not recommended, as later version may damage the phone or have some
- other nasty effect.
-
-
- 4.3. DSLAM
-
- The DSLAM is the equipment at the Telco Central Office that that
- splits the signal and connects the user to the Voice Switch and ISP.
- That's all you need to know from a user perspective.
-
- 4.4. ISP connection
-
- An ISP connects to the DSLAM via a high-speed data connection, usually
- ATM over a T3 (45Mbps) or OC-3 (155Mbps). The important thing here is
- that an ISP must "subscribe" with your Telco to provide this
- connection.
-
-
- 5. Ordering Service
-
- The basic procedure is as follows:
-
- ╖ Check to see if you meet the following requirements for ADSL.
-
- ╖ Select a Telco and ISP, and see what configurations they offer.
-
- ╖ Call the Telco and order the service.
-
- Once you have ordered the service, the Telco should provide you with a
- Due Date. I was able to do the entire order in one phone call through
- my Telco, and they coordinated with the order with my ISP. I was
- given a due date that was one week later, and everything was completed
- on time, with no problems.
-
-
- 5.1. Home Requirements
-
-
- ╖ An appropriate NIC card
-
- The system (PC, workstation, router or hub) that will be directly
- connected to the ADSL ANT .
-
-
- ╖ Inside Wiring
-
- You need inside wire (2 or 4 wire) from the Telco Demarcation Point
- (the side of your house) to your PC location. Your existing phone
- line can be used. However, this inside wire can only be used for
- the ANT, and no other phones or extensions can be connected to this
- line. The Telcos or other companies can be contracted to install a
- new wire for you as well.
-
-
- ╖ Installation
-
-
- Who will wire it up in your house? You can do the splitter wiring
- yourself (My local Telco provided a wiring kit and instructions for
- performing the inside wiring ) or you can contract them do it for
- an additional fee. You can save around $ 150-250 dollars by doing
- it yourself, which I did, or you can save yourself the hassle and
- have them do it. You can decide what you want to do after reading
- the procedure that I have included in this document. The bottom
- line is if you are used to dealing with phone and/or network LAN
- wiring procedures, and feel comfortable with doing this, then you
- should consider going for it. If you haven't, and your company is
- going to pay for it, then have them do it.
-
-
-
- 5.2. Telco Options
-
-
- ╖ Qualified Copper Loop
-
- The Telco will normally test your line before you order service to
- see if it is can pass the ADSL signal. You must be within 2-3
- miles (11-16 kilofeet) of the Central Office, and have a loop that
- has no loading coils, bridge taps, DAMLs, or other impediments.
- Most of the Loops that support ISDN can also support ADSL, but
- since ADSL is more restrictive, this is no guarantee of success.
- Your Telco will help you here.
-
-
- ╖ ADSL Available from your Telco
-
- Is the ADSL/DSLAM equipment is available at your Central Office?
- Again, the Telco will check to see if it available in your area.
- Every major Telco in the US, and many new dedicated ADSL providers
- have announced plans for ADSL. I expect wide scale deployment by
- 1Q99.
-
-
- ╖ Bit Rate
-
- ADSL is priced according to the Bit Rate - Check with your Telco.
- You can usually order some combination of 128k,256k,384k, or 1.5M
- speeds. Your loop may restrict the bit rate you can be offered.
- My Telco also prices the service differently if you're a Residence
- or Business Customer.
-
-
- ╖ POTS Service
-
-
- Some providers (usually the big Telcos) offer POTS with ASDL. If
- you choose this option, you will need to specify which phone number
- (new or existing) you want assigned to it. You will need to
- designation whether you want the ADSL to go over an existing POTS
- service, or whether you want a new phone number for the analog
- phone line. If you have ISDN service, and want to use the same
- line, the ISDN service must first be disconnected. Note that some
- Telcos (usually dedicated DSL providers) do not offer this option.
-
-
-
-
- 5.3. ISP Options
-
-
- ╖ ISP Presubscription
-
- Your ISP of choice must be presubscribed with the ADSL Telco
- provider. Check with your ISP to see if they are connected. If
- they are not connected then you must either move to another ISP,
- convince them to connect up, or decide not to use ADSL.
-
-
-
- ╖ IP Subnet and Address.
-
- First, you'll need to know whether your IP addressing will be
- static or dynamic. Dynamic addressing is set through the use of
- DHCP.
-
- Additionally, for static addressing, ISPs will allow anywhere from
- 1 to 254 IP addresses to be assigned to an ADSL line, with the
- corresponding Variable Length Subnet Mask (VLSM).
-
- My ISP charges more money as you get more hosts. I suspect that
- most applications will use either 1 host (32 bit mask) or 6 hosts
- (29 bit mask). If your confused, then read the IP-Subnetting
- HOWTO. Also remember than multi-host subnets require 1 of the
- hosts to be the ISP router address (meaning that the 6 host subnet
- is really 5 hosts to you) and you can use IP Masquerading/ (see the
- HOWTO) or Network Address Translation (NAT) to support a larger
- number of addresses behind your LAN. If you request more than 30
- hosts, be prepared to fill out a justification form for your ISP.
-
-
- ╖ Gateway Address
-
- The default gateway address. Normally, this is the first host
- address in your subnet. (e.g. if your subnet range and mask is
- 192.168.1.240/29, then your host range is .241 through .246, with
- the default gateway assigned to the .241 address.
-
-
- ╖ Number of MAC addresses
-
- The ANTs can support a set number of MAC addresses for bridging.
- For example, the ADSL ANT that I use is limited to 16 MAC
- addresses. This should be sufficient for most applications.
- However, if you plan to support a large number of machines directly
- off the hub of the ANT, you should check first to see what your
- limit is.
-
-
- ╖ DNS Servers
-
- The ISP should provide you with one or more DNS server addresses to
- support Domain Name Lookups. Some ISPs also provide Domain Name
- Server hosting (either primary or secondary server) for you as part
- of the dedicated service packages. See your ISP for more details.
-
-
- ╖ User ID and Password.
-
- The ISP will normally assign you a login/password for shell, mail,
- etc. access. My ISP also provides web space, mail server, and some
- other goodies.
-
-
-
-
- 6. Wiring it up
-
- If you have ordered the installation option from the Telco, then you
- can skip this section and move to " Configuring Linux" . The
- following procedures are meant to illustrate the wiring process.
- Please note that your procedures may be different at your location.
- Make sure you follow any warnings or safety instructions provided, and
- that you are familiar with Telco wiring procedures.
-
- The first step will be to wire up the connections from your Telco.
- Identify the line on which service will be installed, and the
- locations of your splitter and DSL jacks.
-
- 6.1. Wire the Splitter/NID (at the SNI)
-
- If you have the splitterless design, you can skip this part.
-
- The splitter will consist of two parts, the splitter and a small
- outdoor housing, called the Network Interface Device. Mount the
- splitter and NID housing per the Telcos instructions at the Subscriber
- Network Interface (SNI) point, usually the side of your house where
- the phone line is located. The phone company will need to access the
- splitter for maintenance, so its advisable to locate it on the outside
- where they can get at it. Connect the incoming 2W Telco line to the "
- LINE"side of the splitter. Then wire the inside pair for your
- telephone to the "VOICE" , and your inside wire pair for the ANT to
- "DATA".
-
- Checkstep At this point, you should be able to pull dial tone off the
- voice side of the splitter. If this doesn't work, then either you've
- wired it wrong, or the ADSL service is not yet connected on the Telco
- side.
-
-
- 6.2. Wire the DSL Jack (at the computer location)
-
- Wire up the DSL jack (RJ11) at your computer location (connected to
- the DATA side of the splitter). The specifics differ greatly for each
- situation, but basically you will have a 2 wire pair that you will
- connect to the DSL jack. Make sure you read the directions, as the
- DSL-RJ11 wiring is different for phones and ADSL jacks. In my case,
- you wire the phone jack on the red/green pair (the two inside prongs
- of the RJ11 jack) and the ADSL jack is wired on the yellow/black pair
- (the two outside prongs of the RJ11 jack).
-
- 6.3. Install the ANT (at the computer location)
-
- Connect up the ANT's power cord, and connect the phone line (category
- 3 cable) between the DSL jack and the ANT. This cable is usually
- provided.
-
- Checkstep At this point, verify the ANT syncs up to the Telco signal.
- Most ANTs have an green LED that lights up when the signal is good.
- If it doesn't sync, then check your wiring, or make sure that the
- Telco signal is being sent (do this by calling your Telco and
- verifying they have activated the service. Note that having dial tone
- on the line does NOT confirm the presence of the ADSL data signal.)
-
- If you have completed the previous steps, you are now ready to move on
- to connecting your Linux System.
-
-
- 7. Configuring Linux
-
- After you have wired up the ANT and you're getting the sync signal,
- then you're ready to configure your Linux System and verify your
- connection to your ISP. Although I will refer to a Linux System, you
- can connect any type of 10baseT device to the ANT. This includes a
- router, hub, PC, or any other system that you wish to use.
-
- Caution! Before you connect to your ISP, make sure you understand all
- security issues of having a direct connection to the Internet via
- ADSL. Depending on your ISP, most outside uses can access your
- systems, and you should setup any firewalls, deactivate
- ports/services, and setup any passwords prior to connecting your
- machine to the world. Read the Security-HOWTO if you need a good
- overview on this subject.
-
-
- 7.1. Install and Connect the NIC card
-
- Install your NIC card in your Linux machine, configure the kernel,
- etc., etc. See the various Linux references for doing this. See the
- Ethernet-HOWTO for more information.
-
- Connect the RJ45 cable between the NIC and the ANT. Note A gotcha here
- is that some ANTs are already wired as a 10baseT crossover, and
- require a direct Category 5 cable for a direct connection to a NIC,
- rather than a crossover cable. I lost around 12 hours figuring this
- one out, so don't make the same mistake - make sure you read the
- instructions first.
-
-
- 7.2. Configure the Ethernet Interface
-
- Configure the IP address, Subnet Mask, Default Gateway, and DNS server
- information. Each Linux Distribution (RH, debian, Slackware,
- S.U.S.E.) has a different way of doing this, so check on your
- particulars. You can also do this manually using the ifconfig and
- route commands. See the NET3-HOWTO for information for more
- information.
-
- Once your system is configured, see if you can ping to the your
- default gateway address provided by the ISP. If the ping is
- successful, the you should see around 20 ms roundtrip delay for this
- connection. Congratulations, you're connected to the Net!
-
-
- 7.3. Setting up a Router
-
- Depending on your local setup, you should consider some other issues.
- These include a firewall setup, and any associated configurations.
- For my setup, shown in Figure 3, I use an old i486 machine configured
- as a firewall/router between the ADSL connection and the rest of my
- machines. I use private IP addresses on my Private LAN subnet, and
- have configured my router to provide IP Masquerading and Firewalling
- between the LAN and Internet connection. See the IP_Masquerading-
- HOWTO, and Firewall-HOWTO for more information. My experience is that
- Linux provides superior routing/firewalling performance , and is much
- cheap than a commercial router, if you find an old 386/486 machine
- that you may be using as a doorstop somewhere.
-
-
-
- Figure 3: My SOHO Network Setup
-
-
- <-Private Subnet--> <-Public Subnet-> <-ADSL Line--------->
- |
- X----|
- |
- X------| X----| |----|
- | |--------| | |ADSL| Internet
- | | Linux | |-----|ANT |----------> Service
- X------|------| System |--------| | | Provider
- | E1|(Router)|E0 | |----| Router
- | |--------| |
- X------| IP_Masq 10baseT
- IP_Firewall Hub
-
-
-
-
- What I did is setup a router (Linux RH 5.0 on a i486) with two
- Ethernet interfaces. One interface routes to the ISP subnet/gateway,
- and the other interface supports a class private network address
- (i.e. 192.168.2.x). Using the private network address behind your
- router allows some additional security because it is not directly
- addressable from outside your ISP. You have to explicitly masquerade
- your private addresses in order to connect to the Internet.
-
- Caution Make sure your kernel is complied with IP forwarding and the
- IP forwarding is turned on. You can check this by
-
- cat /proc/sys/net/ipv4/ip_forward
-
-
- The value is "1" for on, and "0" for off. You can change this value
- by echoing the desired value into this file.
-
- (e.g.) echo 1 > /proc/sys/net/ipv4/ip_forward
-
-
- Will turn forwarding on.
-
-
- 7.4. Setting up a Firewall/Masquerading
-
- If you have a direct connection to the Internet, then you want to also
- turn on Firewall Administration and Masquerading. Figure 4 shows a
- picture of this.
-
- Caution! I also need to stress that this configuration is only part
- of the things that need to be performed to create a secure
- environment. Other considerations include turning off ftp, telnet, and
- other services on the Router, and ensuring all password, login, etc.
- configurations are correctly setup for your environment. Make sure
- you read the Security-HOWTO.
-
- Figure 4: Firewall/Masquerading for ADSL
-
- |-------| |-------| |-X
- ======X| ADSL |=------| Linux |-----|
- ADSL | ANT | E0| |E1 |-X Private Network
- Line |-------| |-------| | (e.g. 192.168.2.x)
- <-------> |...
- ISP Subnet or host
- (Public Net Address)
-
-
-
- The kernel for the Linux router is complied for IP
- forwarding/masquerading, and has the "ipfwadm" (IP firewall software)
- installed with the following options:
-
- file: /etc/rc.d/rc.firewall (called by rc.sysinit in RH5.0)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- echo "Setting up the firewall"
- #
- # From the "Firewall-HOWTO"
- #
- # flushes all setting
- #
- ipfwadm -F -f
- #
- # set the firewall
- #
- ipfwadm -F -p deny
- #
- # allow any machine with address 192.168.2.x to masquerade.
- #
- ipfwadm -F -a accept -m -S 192.168.2.0/24 -D 0.0.0.0/0
- #
- # allow the domain name server to work (udp 53)
- #
- ipfwadm -F -a accept -b -P udp -S 0.0.0.0/0 53 -D 192.168.2.0/24
- ipfwadm -F -p masquerade
- #
- # the rest just list out the options for your enjoyment
- #
- ipfwadm -F -l
- ipfwadm -O -l
- ipfwadm -I -l
-
-
-
- You need to be careful, as some application will still not work
- without special modules (namely ftp, real audio, and some others).
- Check the ipfwadm documentation for more information. I found this
- pretty easy to set up.
-
- Additionally, using the private network addressing scheme is cheap,
- and gives an administrator complete flexibility in setting up their
- local LAN. The drawback is that Masquerading has a limit on the
- number of private hosts that it can reasonably support, and that some
- IP applications that pass the host address in their data fields will
- not work, but this tends to be a limited number.
-
-
- 8. Appendix
-
- 8.1. FAQs
-
- This is the Frequently Asked Questions (FAQ) section for ADSL.
-
-
- 1. Q: Are there ADSL Standards.
-
- A: Sort of. The U.S. Bell Operating Companies have standardized on
- Discrete Multi-Tone (DMT) ANTs (ANSI T1.413) in their current
- rollout. Most others should follow their lead in the states. There
- are other types of ANTs, most notably Carrier-less Amplitude Phase
- Modulation (CAP), which, of course, are incompatible with each
- other.
-
- A biased comparison from an DMT-based vendor on this subject can be
- found at the Aware <http://www.aware.com>. Still, it provides the
- best detail on this issue I have seen so far.
-
- A rather expensive copy of the ANSI standard can be ordered at:
- American National Standards Institute ANSI Home Page
- <http://www.ansi.org>
- Asymmetric Digital Subscriber Line (ADSL) Metallic Interface
- ANSI TI.413-1995
- Note: ANSI TI.413 Issue 2 was released September 26, 1997
-
-
- 2. Q: Can I use ATM to connect to ADSL ANT?
-
- A: Yes, you can! Some ADSL ANT (at least the Alcatel version) has a
- ATM Forum 25Mbps interface, which connects to a PCI NIC card.
- However, I have not yet heard of any Linux drivers for such cards.
-
-
- 3. Q: Why the heck does ADSL have all these bit rates
- (384/1.5/8M/20M/etc) options?
-
- A: The basic problem is the 100 year old design of the copper loop.
- It works great for analog phone, but it presents a real challenge
- for a digital signal. Remember that the distance of a loop is
- inversely proportional to the data rate that it can carry. Rate-
- Adaptive technologies are great for making a digital signal work in
- many situations, but it can't provide a consistent bandwidth for
- all applications, especially for very long (over 18 kilofeet)
- loops. The different bandwidth that you see advertised reflect
- various marketing wars of vendors equipment, and the Telco struggle
- to finalize on a ''standard'' set of data rates. I think that the
- 384k/1.5Mbps will become the standard for now. The high bit rates
- will only be available for special application and/or situations,
- since they can only be provided on a small percentage of the
- available loops.
-
- Also, check out the next question on the loop imparments that cause
- this to happen.
-
-
- 4. Q: What are all these loop imparments (bridge taps, loading coils)
- that could disqualify my line from using ADSL? (thanks to Bruce
- Ediger)
-
- Load coils: in-line inductances that improve voice-frequency
- transmission characteristics of a telephone circuit. Essentially,
- a "load" steals energy from high frequencies and gives it to lower
- frequencies. Typically only used in very long (>9,000 ft) phone
- lines.
-
- By "bridges" I assume you mean "bridged taps". In older
- neighborhoods, the phone wiring will have been used by more than
- one customer. Perhaps these customers lived at different (though
- near-by) addresses. The unconnected "spur" of wiring is a "bridged
- tab" on the currently connected circuit.
-
- Digital loop carriers: there's a bunch of systems for carrying more
- than one voice transmission on a single pair of wires. You can
- shift the frequencies up or down, or you can digitize the voice
- transmissions and divide the telephone circuit by time or code or
- something. The more general term is "pair gain".
-
- These things cause different problems for high-frequency
- communication.
-
- Loads will completely mess up things by filtering high frequencies
- and passing low frequencies. They probably also change the "delay
- envelope", allowing some frequencies to arrive before others. One
- byte's tones will interfere with the next byte's.
-
- Bridged taps act as shunt capacitances if they're long in relation
- to the signals wavelength, and they'll actually act as band pass
- filters if they're about 1/4 wavelength of the signal. That is,
- they'll pass particular frequencies freely. Particular tones of a
- DMT modem might get shunted back, rather than passed along to the
- receiving modem, reducing bandwidth for that telephone line.
-
- Pair gain, digital or analog, limit the bandwidth available to one
- transmission in order to multiplex several on one wire. High and
- low tones of a DMT transmission get filtered out by the apparatus.
-
- The book "Subscriber Loop Signaling and Transmission Handbook", by
- Whitham D. Reeve, , IEEE Press 1992, ISBN 0-87942-274-2 covers the
- math of how to calculate the effect of line length, bridged tap,
- etc on the transmission characteristics of a telephone line. It's
- pretty expensive, however.
-
-
- 5. Q: Do you have examples of ADSL ANTs?
-
- A: Short Answer: Yes. Real Answer: The evolution of this technology
- is moving too rapidly for anyone to keep up to date in a HOWTO. A
- good source of ADSL ANTs is the ADSL Forum Home Page
- <http://www.adsl.com>. Go to the Vendors pages to see what's
- happening.
-
- However, I will provide a list of some of the current technology as
- of June 1998.
-
-
-
- ╖ Router ANT with 10/100baseT Interface
-
-
- Examples: Flowpoint 2000 DSL (CAP), Netspeed Speedrunner 202 (CAP),
- Speedrunner 204 (CAP), 3COM Viper-DSL (CAP), StarNet Ezlink 500/100
- (DMT), Westell ATU-R-Flexcap (CAP), Aware x200
-
-
- ╖ Bridge ANT with 10/100baseT Interface
-
- Examples: Alcatel A1000 (DMT), Westell ATU-R-Flexcap2 (CAP)
-
-
- ╖ ANT with ATMF Interface
-
- Examples: Alcatel A1000 (DMT), Netspeed Speedrunner 203 (CAP),
- Ariel Horizon II
-
-
- ╖ Bridge ANT with V.35 Serial Interface (T1, Serial Router)
-
- Examples: Westell ATU-R
-
-
- ╖ ANT with USB Interface
-
-
- Rumored to being pushed by Intel.
-
-
- ╖ Integrated ANT/NIC Card
-
- Examples: Netspeed PCI Runner (CAP), Efficient Networks Speedstream
- 3020 (DMT)
-
- These are NOT endorsements of the products listed, just provided
- for illustration.;-).
-
- 8.2. Links
-
-
- ╖ ADSL Forum Home Page <http://www.adsl.com> A comprehensive web site
- created by the adsl vendors. Fairly complete for reference
- information on ADSL.
-
-
- ╖ Dan Kegels ADSL Page
- <http://www.alumni.caltech.edu/~dank/isdn/adsl.html> A good general
- reference on xDSL - includes vendor, service provider, and other
- links. This page was getting a little long in the tooth as of 2Q98.
- Dan also maintains a super page on ISDN.
-
-
- ╖ PacBell's ADSL Page
- <http://www.pacbell.com/products/business/fastrak/adsl/index.html>
- Pacific Bell is the local Telco and my provider of ADSL service.
-
-
-
- ╖
-
- ╖ Jeremie's Unofficial Ameritech ADSL FAQ
- <http://www.rc.lsa.umich.edu/~jeremie/adsl/>
-
-
- ╖ Telechoice xDSL News Page
- <http://www.telechoice.com/xdslnewz/indexDSL.cgi>
-
-
- ╖ ADSL Deployment 'round the World
- <http://www.geocities.com/Paris/Metro/5013/adsl.html> Claims to
- have a complete list - looked accurate for my area - gives
- providers, prices, speeds, etc.
-
-
- ╖ Bell Atlantic ADSL Home Page <http://www.bell-atl.com/adsl>
-
-
- ╖ comp.dcom.xdsl FAQ <http://homepage.interaccess.com/~jkristof/xdsl-
- faq.txt>
-
-
-
- 8.3. Credits
-
- Thanks to all those that contributed information to this HOWTO. I
- have anti-spammed their email addresses for their safety (and mine!).
- Remove the X's from their names.
-
-
- ╖ B Ediger (Xbediger@csn.net) Great Description of loop impairment.
-
- ╖ C Wiesner ( Xcraig@wkmn.com) List of many ADSL URLs.
-
- ╖ J Leeuw ( Xjacco2@dds.nl) Many tips on ADSL, especially in Europe
-
- ╖ J Kass ( Xjeremie@umich.edu) Unoffical Ameritech ASDL FAQ
-
- ╖ N Silberstein ( Xnick@tpdinc.com) Info on Netrunner and his
- experience with US Worst.
-
-
-
-
- 8.4. Glossary
-
- A dictionary of some of the jargon I use in this FAQ.
-
- 2 wire Copper Loop
- The two wire twisted pair from the Telco Central Office that
- terminates at a customer location.
-
-
- ADSL
- Asymmetric Digital Subscriber Line
-
-
- ANT
- ADSL Network Termination (a.k.a. the ADSL modem)
-
-
- ATM
- Asynchronous Transfer Mode - provides high-speed packet
- switching from 155 Mbps to (currently) 2Gbps. Used to provide
- backbone switching for the Internet.
-
-
- ATMF-25Mbps
- ATM Forum Interface - 25Mbps speed, provided by a PCI NIC card..
- One of the interfaces used between the ANT and PC.
-
-
- Central Office
- Usually refers to one of two meanings -1) The Telco Building
- that houses Telephone equipment 2) The Telco Voice Switch that
- provides dial tone.
-
-
- CPE
- Customer Premises Equipment - The Telco term for customer
- equipment (i.e. the stuff you are responsible for fixing).
- Examples are CSU/DSU, modems, ANTs, and your phone.
-
-
- DHCP
- Dynamic Host Configuration Protocol - The IP protocol used to
- set up dynamically assigned IP addresses.
-
-
- DS0
- The basic digital circuit for Telcos - offered at 56 kbps or
- 64kbps. Can support one analog voice channel.
-
-
- DSLAM
- Digital Subscriber Line Access Multiplexer - The Telco equipment
- that concentrates and multiplexes the DSL lines.
-
-
- xDSL
- Digital Subscriber Line - A term describing a family of DSL
- services, including ADSL, SDSL, VDSL, etc.
-
-
- HDC
- See Section 2
-
-
- ISDN
- Innovations Subscribers Don't Need; I Still Don't kNow or maybe
- Integrated Services Digital Network, a digital phone service
- that uses a single copper pair to run 2B (64k) + 1D(16k)
- channels that can be used for switched voice or data.
-
-
- ISP
- Internet Service Provider
-
-
- NID
- Network Interface Device - The housing used to protect the ADSL
- splitter from the elements.
-
-
- NIC
- Network Interface Card - A PC card (PCI/ISA) that supports the
- required network interface. Usually an Ethernet 10baseT or an
- ATMF-25Mbps Card..
-
-
- POTS
- Plain Old Telephone Service - The service that provides a single
- analog voice line. (i.e. your phone line)
-
-
- Recursion
- See "Recursion"
-
-
- SNI
- Subscriber Network Interface - The Telco term for the phone
- wiring housing on the side of your house. It designates the
- point between the Telco side and the Inside Wire. This is also
- called the Demarcation Point.
-
-
- Splitter
- The passive device (low-bandpass filter) at the SNI that splits
- the ADSL signal into separate voice and data channels.
-
-
- Splitterless
- An ADSL installation that does not require the Splitter. For
- higher speeds, a RJ11 filter is placed on every extension phone
- jack where an analog phone is used, thus providing the filtering
- at the jack, rather than at the NID. For lower speeds, no
- filter is required.
-
-
- SOHO
- Small Office HOme
-
-
- T1 a.k.a DS1 - A digital dedicated line at 1.544 Mbps, used for
- both Voice (24 DS0s) or Data.
-
-
- T3 a.k.a DS3 - A digital dedicated line at 44.736 Mbps, provides
- for both Voice (672 DS0s or 28 DS1s) or Data
-
-
-
-
-
-
-
-