Hackers Handbook - Millenium Edition

home *** CD-ROM | disk | FTP | other *** search

/ Hackers Handbook - Millenium Edition / Hackers Handbook.iso / files / hfiles / dhcp-faq.txt < prev next >

Wrap

Text File | 1997-09-25 | 43.4 KB | 827 lines

DHCP FAQ Author John Wobus, jmwobus@syr.edu (corrections welcome) Date 3/28/96 This file http://web.syr.edu/~jmwobus/comfaqs/dhcp.faq.html Questions 1. General 1. What is DHCP? 2. What is DHCP's purpose? 3. Who Created It? How Was It Created? 4. How is it different that BOOTP or RARP? 5. Why shouldn't clients assign IP numbers without the use of a server? 6. Can DHCP support statically defined addresses? 7. Can a BOOTP client boot from a DHCP server? 8. Can a DHCP client boot from a BOOTP server? 9. Is a DHCP server "supposed to" be able to support a BOOTP client? 10. Is a DHCP client "supposed to" be able to use a BOOTP server? 11. Can a DHCP client update its DNS entry through DHCP? 12. Can a DHCP server back up another DHCP server? 13. When will the server to server protocol be defined? 14. Is there a DHCP mailing list? 15. In a subnetted environment, how does the DHCP server discover what subnet a request has come from? 16. Where is DHCP defined? 17. What other sources of information are available? 18. Can DHCP support remote access? 19. Can a client have a home address and still float? 20. How can I relay DHCP if my router does not support it? 21. How do I migrate my site from BOOTP to DHCP? 22. Can you limit which MAC addresses are allowed to roam? 23. What are the Gotcha's? 2. Info on Implementations 1. What features or restrictions can a DHCP server have? 2. What freeware DHCP servers are available? 3. What commercial DHCP servers are available? 4. Which vendors of client software currently support DHCP? 5. What are the DHCP plans of major client-software vendors? 6. What Routers forward DHCP requests? 7. What Routers include DHCP servers? 8. What Servers forward DHCP requests? 9. Which implementations support or require the broadcast flag? 10. How can I run Windows 95 without a DHCP server? 11. Do any servers limit the MAC addresses that may roam? 12. What are the Gotcha's specific to various implementations? Answers 1. General 1. What is DHCP? DHCP stands for "Dynamic Host Configuration Protocol". 2. What is DHCP's purpose? DHCP's purpose is to enable individual computers on an IP network to extract their configurations from a server (the 'DHCP server') or servers, in particular, servers that have no exact information about the individual computers until they request the information. The overall purpose of this is to reduce the work necessary to administer a large IP network. 3. Who Created It? How Was It Created? DHCP was created by the Dynamic Host Configuration Working Group of the Internet Engineering Task Force (IETF; a volunteer organization which defines protocols for use on the Internet). As such, it's definition is recorded in an Internet RFC and the Internet Activities Board (IAB) is asserting its status as to Internet Standardization. As of this writing (March 1996), DHCP is an Internet Proposed Standard Protocl and is Elective. BOOTP is an Internet Draft Standard Protocol and is Recommended. For more information on Internet standardization, see RFC1920 (March 1996). 4. How is it different that BOOTP or RARP? DHCP is based on BOOTP and maintains some backward compatibility. The main difference is that BOOTP was designed for manual pre-configuration of the host information in a server database, while DHCP allows for dynamic allocation of network addresses and configurations to newly attached hosts. Additionally, DHCP allows for recovery and reallocation of network addresses through a leasing mechanism. RARP is a protocol used by Sun and other vendors that allows a computer to find out its own IP number, which is one of the protocol parameters typically passed to the client system by DHCP or BOOTP. RARP doesn't support other parameters and using it, a server can only serve a single LAN. DHCP and BOOTP are designed so they can be routed. 5. Why shouldn't clients assign IP numbers without the use of a server? It is theoretically possible for client-machines to find addresses to use by picking an address out of the blue and broadcasting a request of all the other client machines to see if they are using them. Appletalk is designed around this idea, and Apple's MacTCP can be configured to do this for IP. However, this method of IP address assignment has disadvantages. 1. A computer that needs a permanently-assigned IP number might be turned off and lose its number to a machine coming up. This has problems both for finding services and for security. 2. A network might be temporarily divided into two non-communicating networks while a network component is not functioning. During this time, two different client-machines might end up claiming the same IP number. When the network comes back, they start malfunctioning. 3. If such dynamic assignment is to be confined to ranges of IP addresses, then the ranges are configured in each desktop machine rather than being centrally administered. This can lead both to hidden configuration errors and to difficulty in changing the range. Another problem with the use of such ranges is keeping it easy to move a computer from one subnet to another. 6. Can DHCP support statically defined addresses? Yes. At least there is nothing in the protocol to preclude this and one expects it to be a feature of any DHCP server. This is really a server matter and the client should work either way. The RFC refers to this as manual allocation. 7. Can a BOOTP client boot from a DHCP server? Only if the DHCP server is specifically written to also handle BOOTP queries. 8. Can a DHCP client boot from a BOOTP server? Only if the DHCP client were specifically written to make use of the answer from a BOOTP server. It would presumeably treat a BOOTP reply as an unending lease on the IP address. In particular, the TCP/IP stack included with Windows 95 Does not have this capability. 9. Is a DHCP server "supposed to" be able to support a BOOTP client? The RFC on such interoperability (1541) is clear: "In summary, a DHCP server: ... MAY support BOOTP clients," (section 2). The word "MAY" indicates such support, however useful, is left as an option. 10. Is a DHCP client "supposed to" be able to use a BOOTP server? The RFC on such interoperability (1541) is clear: "A DHCP client MAY use a reply from a BOOTP server if the configuration returned from the BOOTP server is acceptable to the DHCP client." (section 3). The word "MAY" indicates such support, however useful, is left as an option. 11. Can a DHCP client update its DNS entry through DHCP? No. There has been some discussion about adding this ability to DHCP. (Note: as far as I can tell, the DNS needs no protocol update since the server already tells the clients how long they can use the information they receive; what is really needed is a DNS server that can make fuller use of this feature and that cooperates with a DHCP server, perhaps through the use of some new "DHCP-server-to-DNS-server" protocol). 12. Can a DHCP server back up another DHCP server? This is the purpose of the "server to server protocol" (see next question). I know of no other way that you can keep a "hot" spare server in synch with your production server. However, it is possible that some server vendors have addressed this issue with their own features. 13. When will the server to server protocol be defined? The DHC WG of the IETF is actively investigating the issues in inter-server communication. The protocol should be defined "soon". 14. Is there a DHCP mailing list? There are several: List Purpose ---- ------- dhcp-v4@bucknell.edu General discussion: a good list for server administrators. dhcp-bake@bucknell.edu DHCP bakeoffs dhcp-impl@bucknell.edu Implementations dhcp-serve@bucknell.edu Server to server protocol dhcp-dns@bucknell.edu DNS-DHCP issues dhcp-v6@bucknell.edu DHCP for IPv6 The lists are run by listserv@bucknell.edu which can be used to subscribe and sign off. Archives for the dhcp-v4 list (which used to be called the host-conf list) are stored at ftp://ftp.bucknell.edu/pub/dhcp/. 15. In a subnetted environment, how does the DHCP server discover what subnet a request has come from? DHCP client messages are sent to off-net servers by DHCP relay agents, which are often a part of an IP router. The DHCP relay agent records the subnet from which the message was received in the DHCP message header for use by the DHCP server. Note: a DHCP relay agent is the same thing as a BOOTP relay agent, and the latter phrase is more commonly used. 16. Where is DHCP defined? In Internet RFCs. RFC1541 R. Droms, "Dynamic Host Configuration Protocol", 10/27/1993. RFC1534 R. Droms, "Interoperation Between DHCP and BOOTP", 10/08/1993. RFC1533 S. Alexander, R. Droms, "DHCP Options and BOOTP Vendor Extensions", 10/08/1993. A web site for RFCs is: http://ds.internic.net/ds/dspg1intdoc.html 17. What other sources of information are available? See the dhcp-v4 mailing list mentioned above as well as its archives. DHCP - Dynamic Host Configuration Protocol http://www.bucknell.edu/~droms/dhcp/ Problems and Solutions of DHCP: Experiences with DHCP implementation and Operation A. Tominaga, O. Nakamura, F. Teraoka, J. Murai. http://info.isoc.org/HMP/PAPER/127/html/paper.htm l DHCP Resources Alan Dobkin. http://NWS.CC.Emory.Edu/WebStaff/Alan/Net-Man/Com puting/DHCP/ Internet Drafts Internet drafts are works in progress intended to update the current RFCs or specify additional functionality, and sometimes there is one or more draft related to DHCP. All Internet Drafts are available from various sites: the US East Cost site is ftp://ds.internic.net/internet-drafts/; a web site is http://ds.internic.net/ds/dsintdrafts.html. The DHCP-related drafts currently have filenames of the form "draft-ietf-dhc-SOMETHING". These DHCP-related drafts are also stored at ftp://ftp.bucknell.edu/pub/dhcp/, and are available through http://www.bucknell.edu/~droms/dhcp/. I cannot be more specific about the documents because they are by their nature temporary. 18. Can DHCP support remote access? PPP has its own non-DHCP way in which communications servers can hand clients an IP address called IPCP (IP Control Protocol) but doesn't have the same flexibility as DHCP or BOOTP in handing out other parameters. Such a communications server may support the use of DHCP to acquire the IP addresses it gives out. This is sometimes called doing DHCP by proxy for the client. I know that Windows NT's remote access support does this. A feature of DHCP under development (DHCPinform) is a method by which a DHCP server can supply parameters to a client that already has an IP number. With this, a PPP client could get its IP number using IPCP, then get the rest of its parameters using this feature of DHCP. SLIP has no standard way in which a server can hand a client an IP address, but many communications servers support non-standard ways of doing this that can be utilized by scripts, etc. Thus, like communications servers supporting PPP, such communications servers could also support the use of DHCP to acquire the IP addressees to give out. I am not currently aware of any way in which DHCP can support client-computers served solely by PPP or SLIP. Such a computer doesn't have the IEEE-style MAC address that DHCP requires to act as its key to determining which client-computer is which within the same subnet. Communications servers that acquire IP numbers for their clients via DHCP run into the same roadblock in that they have just one MAC address, but need to acquire more than one IP address. One way such a communications server can get around this problem is through the use of a set of unique pseudo-MAC addresses for the purposes of its communications with the DHCP server. Another way (used by Shiva) is to use a different "client ID type" for your hardware address. Client ID type 1 means you're using MAC addresses. However, client ID type 0 means an ASCII string. 19. Can a client have a home address and still float? There is nothing in the protocol to keep a client that already has a leased or permanent IP number from getting a(nother) lease on a temporary basis on another subnet (i.e., for that laptop which is almost always in one office, but occiasionally is plugged in in a conference room or class room). Thus it is left to the server implementation to support such a feature. I've heard that Microsoft's NT-based server can do it. 20. How can I relay DHCP if my router does not support it? A server on a net(subnet) can relay DHCP or BOOTP for that net and Windows NT is an example of a server with that capability. 21. How do I migrate my site from BOOTP to DHCP? I don't have an answer for this, but will offer a little discussion. The answer depends a lot on what BOOTP server you are using and how you are maintaining it. If you depend heavily on BOOTP server software to support your existing clients, then the demand to support clients that support DHCP but not BOOTP presents you with problems. In general, you are faced with the choice: 1. Find a server that is administered like your BOOTP server only that also serves DHCP. For example, one popular BOOTP server, the CMU server, has been patched so that it will answer DHCP queries. 2. Run both a DHCP and a BOOTP server. It would be good if I could find out the gotcha's of such a setup. 3. Adapt your site's administration to one of the available DHCP/BOOTP servers. 4. Handle the non-BOOTP clients specially, e.g. turn off DHCP and configure them statically: not a good solution, but certainly one that can be done to handle the first few non-BOOTP clients at your site. 22. Can you limit which MAC addresses are allowed to roam? Sites may choose to require central pre-configuration for all computers that will be able to acquire a dynamic address. A DHCP server could be designed to implement such a requirement, presumeably as an option to the server administerator. See section below on servers that implement this. 23. What are the Gotcha's? o A malicious user could make trouble by putting up an unofficial DHCP server. # The immediate problem would be a server passing out numbers already belonging to some computer yielding the potential for two or more "innocent bystander" nodes ending up with the same IP number. Net result is problems using the nodes, possibly intermittent of one or the other is sometimes turned off. # A lot of problems are possible if a renegade server manages to get a client to accept its lease offering, and feeds the client its own version of other booting parameters. One scenario is a client that loads its OS over the network via tftp being directed to a different file (possibly on a different server), thus allowing the perpetrator to take over the client. Given that boot parameters are often made to control many different things about the computers' operation and communication, many other scenarios are just as serious. Note that BOOTP has the same vulnerabilities. o The "broadcast flag": DHCP includes a way in which client implementations unable to receive a packet with a specific IP address can ask the server or relay agent to use the broadcast IP address in the replies (a "flag" set by the client in the requests). The definition of DHCP states that implementations "should" honor this flag, but it doesn't say they "must". Some Microsoft TCP/IP implementations used this flag, which meant in practical terms, relay agents and servers had to implement it. A number of BOOTP-relay-agent implementations (e.g. in routers) handled DHCP just fine except for the need for this feature, thus they announced new versions stated to handle DHCP. o Some of the virtual LAN schemes, i.e., those that use the packet's IP number to decide which "virtual LAN" a client-computer is on for the purposes of TCP/IP, don't work when using DHCP to dynamically assign addresses. DHCP servers and relay agents use their knowledge of what LAN the client-station is on to select the subnet number for the client-station's new IP address whereas such switches use the subnet number sent by the client-station to decide which (virtual) LAN to put the station on. o Routers are sometimes configured so that one LAN on one port has multiple network (or subnet) numbers. When the router is relaying requests from such a LAN to the DHCP server, it must pass along as IP number that is associated with one of the network (or subnet) numbers. The only way the DHCP server can allocate addresses on one of the LAN's other network (or subnet) numbers is if the DHCP server is specifically written to have a feature to handle such cases, and it has a configuration describing the situation. o The knowledge that a particular IP number is associated with a particular node is often used for various functions. Examples are: for security purposes, for network management, and even for identifying resources. Furthermore, if the DNS's names are going to identify IP numbers, the numbers, the IP numbers have to be stable. Dynamic configuration of the IP numbers undercuts such methods. For this reason, some sites try to keep the continued use of dynamically allocatable IP numbers to a minimum. o With two or more servers serving a LAN, clients that are moved around (e.g. mobile clients) can end up with redundant leases. Consider a home site with two DHCP servers, a remote site with DHCP services, and a mobile client. The client first connects to the home site and receives an address from one of the two serves. He/she then travels to the remote site (without releasing the lease at the home site) and attempts to use the acquired address. It is of course NAK'ed and the client receives an address appropriate for the remote site. The client then returns home and tries to use the address from the remote site. It is NAK'ed but now the client broadcasts a DHCPDISCOVER to get a address. The server that holds the previous lease will offer the address back to the client but there is no guarantee that the client will accept that address; consequently, it is possible for the client to acquire an address on the other server and therefore have two leases within the site. The problem can be solved by using only one server per subnet/site and can be mitigated by short lease lengths. But in a very mobile environment, it is possible for these transient servers to consume more than their fair share of addresses. 2. Info on Implementations 1. What features or restrictions can a DHCP server have? While the DHCP server protocol is designed to support dynamic management of IP addresses, there is nothing to stop someone from implementing a server that uses the DHCP protocol, but does not provide that kind of support. In particular, the maintainer of a BOOTP server-implementation might find it helpful to enhance their BOOTP server to allow DHCP clients that cannot speak "BOOTP" to retrieve statically defined addresses via DHCP. The following terminology has become common to describe three kinds of IP address allocation/management. These are independent "features": a particular server can offer or not offer any of them: o Manual allocation: the server's administrator creates a configuration for the server that includes the MAC address and IP address of each DHCP client that will be able to get an address: functionally equivalent to BOOTP though the protocol is incompatible. o Automatic allocation: the server's administrator creates a configuration for the server that includes only IP addresses, which it gives out to clients. An IP address, once associated with a MAC address, is permanently associated with it until the server's administrator intervenes. o Dynamic allocation: like automatic allocation except that the server will track leases and give IP addresses whose lease has expired to other DHCP clients. Other features which a DHCP server may or may not have: o Support for BOOTP clients. o Support for the broadcast bit. o Administrator-setable lease times. o Administrator-setable lease times on manually allocated addresses. o Ability to limit what MAC addresses will be served with dynamic addresses. o Allows administrator to configure additional DHCP option-types. o Interaction with a DNS server. Note that there are a number of interactions that one might support and that a standard set & method is in the works. o Interaction with some other type of name server, e.g. NIS. o Allows manual allocation of two or more alternative IP numbers to a single MAC address, whose use depends upon the gateway address through which the request is relayed. o Ability to associate two or more dynamic address pools on separate IP networks (or subnets) with a single gateway address. This is the basic support for "secondary nets", e.g. a router that is acting as a BOOTP relay for an interface which has addresses for more than one IP network or subnet. o Support for User Class Information option. o Support for Vendor Class Information option. o Administrator-setable T1/T2 lengths. o Interaction with another DHCP server. Note that there are a number of interactions that one might support and that a standard set & method is in the works. o Use of PING (ICMP Echo Request) to check an address prior to dynamically allocating it. o Server grace period on lease times. Following are some features related not to the functions that the server is capable of carrying out, but to the way that it is administered. o Ability to import files listing manually allocated addresses (as opposed to a system which requires you to type the entire configuration into its own input utility). Even better is the ability to make the server do this via a command that can be used in a script, rdist, rsh, etc. o Graphical administration. o Central administration of multiple servers. 2. What freeware DHCP servers are available? (This is not necessarily a complete list) 950415 Bootp server: Bootp 2.4.3 (not DHCP, but with the "DHCP patches" mentioned below, can handle DHCP requests) ftp://ftp.mc.com/pub/bootp-2.4.3.tar.Z 950425 Bootp server version 2.4.3 with "samba" DHCP patches (does manual allocation of IP addresses) http://www.sghms.ac.uk/~mpreston/bootp_dhcp.tar.Z (within http://www.sghms.ac.uk/~mpreston/tools.htm") 950706 "samba" DHCP patches for bootp server: (does manual allocation of IP addresses) ftp://nimbus.anu.edu.au:/pub/tridge/samba/contributed/DHCP.patch (note: I've heard that the patched server will crash if it receives one particular optional packet, the DHCP Release packet) 950711 Patched bootp server supporting DHCP-based "automatic" allocation: (gives addresses dynamically, but never takes them away) ftp://ftp.ntplx.net/pub/networking/bootp/bootp-DD2.4.3.tar.gz 951219 BOOTP server and patches for DHCP ftp://africa.geomic.uni-oldenburg.de/pub/people/joey/dhcp/bootpd/ 960112 OS/2 port of BOOTP server with patches for manual DHCP support ftp://ftp.leo.org/pub/comp/os/os2/tcpip/systools/bootpd-243-dhcp.zip 960130 Rose-Hulman Institute of Technology "Mondo-DB" LAN administration project: modified DHCP server planned http://www.rose-hulman.edu/~allard/Mondo-DB/index.html 950630 WIDE Project: Akihiro Tominaga (tomy@sfc.wide.ad.jp) WIDE Project Keio Univ. Japan ftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.2.1.tar.gz Check Archie for dhcp-1.2.1 because lots of sites distribute it. Beta version: ftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.3beta.tar.gz 960308 Internet Software Consortium DHCP/BOOTP Server (ISC dhcpd beta 0) ftp://www.isc.org/pub/dhcp/DHCPD-BETA-0.tar.gz http://www.isc.org/isc 960308 Carnegie Mellon University DHCP/BOOTP server (SunOS, dhcp-3.3.6) ftp://ftp.net.cmu.edu/pub/dhcp/dhcp-3.3.6.tar.gz 3. What commercial DHCP servers are available? (This is not necessarily a complete list) 950425 Silicon Graphics 950613 NetWare/IP 2.1 will NOT support DHCP but support for enhanced bootp will be provided. I'm guessing this means DHCP-format packets, but no address leasing. 950714 FTP Software (Services OnNet Product) http://www.ftp.com/mkt_info/services.html 950714 Microsoft Windows NT http://www.microsoft.com/NTServer/ http://www.microsoft.com/BackOffice/techbriefs/tech1000.htm 950714 Hewlett Packard HP-UX 950906 IBM: included in Warp Server which is in beta 951010 Wollongong: included in next release of PathWay for OpenVMS which is in beta 951010 TGV: DHCP/BOOTP server will be included in Multinet for VMS v3.5. http://www.tgv.com/ 951121 TGV(800-848-3440): MultiNet 3.5 for OpenVMS includes DHCP server. mailto:sales@tgv.com http://www.tgv.com/ 951207 IBM: DHCP server included in AIX 4.1.4 server packages. Also includes custom DNS server that is "DHCP knowledgeable". http://www.ibmlink.ibm.com/(search for DHCP in SalesManual) 951219 Puzzle Systems: WEBserv (NLM(s) that do DHCP, BOOTP, HTTP, and FTP) mailto:info@puzzle.com http://www.puzzle.com/ 951220 ON Technology: IPTrack is a Novell Server-based DHCP/BOOTP server (NLM) http://www.on.com/on/onprods/iptrack.html/ 951220 Process Software: server for OpenVMS included in TCPware for OpenVMS http://www.process.com/ 960108 Sun Solstice LAN Management Package (SolarNet) http://www.sun.com/cgi-bin/show?sunsoft/Products/Networking-products/pro ducts/pcadmin.html http://www.sun.com/cgi-bin/show?products-n-solutions/sw/solstice/network /prod_spec_solstice_solarnet.html 960110 Quadritek Systems, Inc. (DHCP server included in next release) http://www.qtek.com/qsi-qip.html 960130 Network TeleSystems: Shadow (PC-based) http://www.ntsi.com/nts_shadow.html 960130 Digital: RoamAbout Mobile IP Client/Server Network Software V2.0 http://www.digital.com/info/Customer-Update/940620001.txt.html 960208 Competitive Automation's JOIN (415-321-4006): SunOS4.x, Solaris2.x, DECOSF3.x,4.x, HP-UX 9 & 10 DHCP/BOOTP servers. http://www.join.com/ 960209 Microsoft Windows NT Server http://www.microsoft.com/NTServer/ http://www.microsoft.com/BackOffice/techbriefs/tech1000.htm ftp://ftp.microsoft.com/bussys/winnt/winnt-docs/papers/tcpipimp.doc 960312 Nevod Inc. Proxy IP/DHCP Server (PIP) Beta-1.0 http://www.nevod.com/pip/index.html 960327 Xedia: IP/Assist 1.0 feature for their switches includes DHCP service. http://www.xedia.com 960328 Novell: Netware IP 2.2 includes a DHCP server. ftp://ftp.novell.com/updates/unixconn/nwip22/nips22.exe 4. Which vendors of client software currently support DHCP? (This is not necessarily a complete list) 950417 Shiva: proxy client for remote users (in Lanrovers and Netmodems) 950421 Microsoft: Windows for Workgroups 950425 Sun 950425 Silicon Graphics 950425 Hewlett-Packard 950502 NetManage: Chameleon 4.5 950630 Beame & Whiteside Software: resells Dirk Koeppen EDV-Beratungs-GmbH's TCP/IP BOOT-PROM 950705 Microsoft: MS-TCP/IP 3.11a & MS-TCP/IP 3.11b 950711 Microsoft: Windows NT 3.5 950711 Microsoft: Windows for Workgroups 3.11a 950711 Frontier Technologies(800-929-3054): in SuperTCP for Windows http:www.frontiertech.com info@frontiertech.com 950712 Beame & Whiteside(800-720-7151): BW-Connect NFS for DOS & Windows 950725 IBM: a future release of AIX 950728 Sun: PCNFS for Windows 950802 Wollongong: PathWay Access ver 3.2 (Windows) http://www.twg.com/ 950802 WRQ: Reflection Network Series products (version 5) for Windows http://www.wrq.com/ 950814 Competitive Automation(415-321-4006): SunOS4.x, Solaris2.x and DECOSF3.x,4.x clients 950906 IBM: included in Warp Server which is in beta 950915 Stampede: included in Remote Office Gold 951113 Persoft(800-368-5283): TCP Addition and Portable TCP http://www.persoft.com 951207 Dirk Koeppen EDV-Beratungs-GmbH: TCP/IP DHCP Boot ROMs (TCP/IP BOOT-PROM) www.dunkel.de/dksoft 951207 IBM: AIX 4.1.4 client and server packages include a DHCP client. http://www.ibmlink.ibm.com/(search for DHCP in SalesManual) 951220 Attachmate: IRMA TCP Suite Version 3.1 960130 Digital: RoamAbout Mobile IP Client/Server Network Software V2.0 http://www.digital.com/info/Customer-Update/940620001.txt.html 960209 FTP Software: OnNet 2.0 (Windows) http://www.ftp.com/ 960209 FTP Software: PC/TCP 4.0 (DOS) http://www.ftp.com/ 960305 TGV: will be included in MultiNet for Windows V1.2 http://www.tgv.com/ 960312 Core Systems: Internet-Connect for Windows 95 Version 2.1 has DHCP proxy client. http://ns1.win.net/~core/Coresys/homepage.html 960312 Novell: I heard a report that they offer a client. 960313 Apple: Open Transport 1.1 included with System 7.5.3 & runs on 68030, 68040, and PowerPC Macintoshes. 960314 Apple: Open Transport 1.1 shrink wrap version will be offered. 5. What are the DHCP plans of major client-software vendors? Apple MacOS MacTCP's successor, Open Transport, supports DHCP. Open Transport 1.1 ships with System 7.5 Update 2.0 (which updates MacOS to version 7.5.3, released March 11, 1996) and supports any 68030, 68040, or PowerPC Macintosh. A shrink wrap version of Open Transport is planned. Microsoft Windows95 supports it and does not support BOOTP. I heard a rumor that BOOTP support will be added. Novell LAN Workplace for DOS has plans for client support later in 1995. IBM OS/2 will support it; I have no news on when or what version. 6. What Routers forward DHCP requests? (This is not necessarily a complete list). Note that in general, these routers probably already had BOOTP forwarding, but lacked the support for the BOOTP broadcast flag (see "broadcast flag" under What are the Gotcha's? above). It is likely that many other routers also support BOOTP forwarding. Cisco (from Cisco FAQ) Routers running GSYS version 9.21(4) and 10.0(3) as well as later releases. Wellfleet/Bay (from Wellfleet FAQ) DHCP is supported by enabling BOOTP support (with transmission and/or reception as needed). 3Com Netbuilder Version 7.2 software can support DHCP relaying through the use of its generic UDP Helper service. Version 8.0 and later officially supports DHCP. Xyplex Version 5.5 of their routing software supports DHCP. ALANTEC The switches' "router" function has have been handling BOOTP forwarding since around 1993. Support for the broadcast flag introduced in a maintenance release of 2.5 of their software and is in version 2.6 and later. IBM 2210 I've confirmed that Version 1 Release 2 has a BOOTP relay agent. I haven't found out anything about support for the broadcast flag. 7. What Routers include DHCP servers? DHCP requires disk storage (or some other form of reliable non-volatile storage), making the task of DHCP service compatible with servers but incompatible with dedicated routers. There are a number of server types that can be configured to both route and serve DHCP (especially all-in-one "Internet Gateways" designed to be web servers, firewalls, etc.), but no dedicated routers. 8. What Servers forward DHCP requests? o DHCP Relay Agent supplied with Windows NT Resource Kit (version 3.51). o For Novell servers, there are NLMs that forward BOOTP requests, thus DHCP requests. The "forward BOOTP NLM" is included in Netware 4.1. You can get this support in Netware 3.11 and 3.12 also, but you must apply the TCP31A.EXE patch which is located on Netwire. Here are two such NLMs that are available online: # ftp://netlab2.usu.edu/misc/bootpfd.zip(unsupported Novell software, 1993) # ftp://netlab2.usu.edu/misc/bootp311.zip(unsupported Novell software, 1991) 9. Which implementations support or require the broadcast flag? The broadcast flag is an optional element of DHCP, but a client which sets it works only with a server or relay that supports it. o Clients Microsoft Windows NT DHCP client support added with version 3.5 sets the broadcast flag. Version 3.51 and later no longer set it. The exception is in the remote access support: it sets the flag when it uses DHCP to acquire addresses to hand out to its PPP clients. tcp/ip-32 for Microsoft Windows for Workgroups (WFW) Version 3.11a sets it, but version 3.11B doesn't. Microsoft Windows 95 Does not set the broadcast flag. 10. How can I run Windows 95 without a DHCP server? Not really a DHCP question, but it has been asked a lot, particularly by sites for which changing from BOOTP represents a lot of work. Some choices: o Use no server at all for the Windows 95 clients: set the addresses in each client's setup. o Install a non-Microsoft TCP/IP stack for Windows 95 that supports BOOTP. o Switch from your current BOOTP server to one that supports both BOOTP and DHCP. A Document that addresses this question is the Windows 95tm Networking FAQ, http://www-leland.stanford.edu/~llurch/win95netbugs/faq.htm l 11. Do any servers limit the MAC addresses that may roam? o IBM's AIX and OS/2 WARP DHCP servers. 12. What are the Gotcha's specific to various implementations? In many cases, new releases have solved the problems that have been identified with various DHCP implementations. o There have been servers that are inflexible as to the list of configuration parameters they were able to serve. If your client requires certain parameters, you could find such a server unusable. o I hate to cast wide suspicions, but I've heard occasional word on client DHCP implementations that do not implement the entire protocol. Doing so requires that the software module be able to wake up again after a specified period of time and "renew the lease", i.e., ask to continue using the IP number. This is at least one feature of DHCP that is very hard to implement in some simpler systems. o There are a number of issues regarding the patched bootp servers. These have been reported to re DD2.4.3: # 'When run from inetd, I had problems with "Could not bind port" and DHCP request failure. I don't know why, and the problem went away when bootpd is run as a daemon.' # 'Unless you set "dl" to some value in the bootptab file, the DHCP lease time, renewal time and prebinding time will be rubbish, which will cause occasional renewal problems.' o Early Microsoft DHCP client implementations required the broadcast bit. Current ones do not. o Early Apple Open Transport implementations did not always fill out packets to BOOTP's 300-byte minimum, thus BOOTP forwarding agents that follow the BOOTP RFC and discard such packets end up discarding such DHCP packets, causing some of the functions to fail. Open Transport 1.1 fixes this. Posted Mon Apr 1 14:17:39 EST 1996