Internet Software Consortium Dynamic Host Configuration Protocol Distribution Development Snapshot November 22, 1997 This is a development snapshot of work in progress on version 2.0 of the Internet Software Consortium DHCP Distribution. In version 2.0, this distribution includes a DHCP server, a DHCP client, and a BOOTP/DHCP relay agent. The engineering snapshot has become a lot more stable since the last snapshot, and will soon go into beta. However, DHCP server users running a production environment should probably still use the latest version on the 1.0 release branch, which is more stable, having been in a feature freeze since November of 1996. In this release, the server and relay agent currently work well on Digital Alpha OSF/1, SunOS 4.1.4, NetBSD, FreeBSD, BSD/OS and Ultrix. They can also be run usefully on Solaris as long as only one broadcast network interface is configured. They also runs on QNX and Linux as long as only one broadcast network interface is configured and a host route is added from that interface to the 255.255.255.255 broadcast address. If you are running a Linux 2.0.31 kernel, the DHCP daemons may be able to operate on more than one interface. The DHCP client currently only knows how to configure the network on NetBSD, FreeBSD, BSD/os, Linux, Solaris and NextStep. The client depends on a system-dependent shell script to do network configuration - support for other operating systems is simply a matter of porting this shell script to the new platform. If you wish to run the DHCP Distribution on Linux, please see the Linux-specific notes later in this document. If you wish to run on a SCO release, please see the SCO-specific notes later in this document. You particularly need to read these notes if you intend to support Windows 95 clients. If you are running a version of FreeBSD prior to 2.2, please read the note on FreeBSD. If you are running HP-UX or Ultrix, please read the notes for those operating systems below. If you are running NeXTSTEP, please see the notes on NeXTSTEP below. If you start dhcpd and get a message, "no free bpf", that means you need to configure the Berkeley Packet Filter into your operating system kernel. On NetBSD, FreeBSD and BSD/os, type ``man bpf'' for information. On Digital Unix, type ``man pfilt''. BUILDING THE DHCP DISTRIBUTION To build the DHCP Distribution, type ``configure''. If configure can figure out what sort of system you're running on, it will create a custom Makefile for you for that system; otherwise, it will complain. If it can't figure out what system you are using, that system is not supported - you are on your own. Once you've run configure, just type ``make'', and after a while you should have a dhcp server. If you get compile errors on one of the supported systems mentioned earlier, please let us know. If you get errors on a system not mentioned above, you will need to do some programming or debugging on your own to get the DHCP Distribution working. LINUX There are three big LINUX issues: the all-ones broadcast address, Linux 2.1 ip_bootp_agent enabling, and operations with more than one network interface. BROADCAST In order for dhcpd to work correctly with picky DHCP clients (e.g., Windows 95), it must be able to send packets with an IP destination address of 255.255.255.255. Unfortunately, Linux insists on changing 255.255.255.255 into the local subnet broadcast address (here, that's 192.5.5.223). This results in a DHCP protocol violation, and while many DHCP clients don't notice the problem, some (e.g., all Microsoft DHCP clients) do. Clients that have this problem will appear not to see DHCPOFFER messages from the server. It is possible to work around this problem on some versions of Linux by creating a host route from your network interface address to 255.255.255.255. The command you need to use to do this on Linux varies from version to version. The easiest version is: route add -host 255.255.255.255 dev eth0 On some older Linux systems, you will get an error if you try to do this. On those systems, try adding the following entry to your /etc/hosts file: 255.255.255.255 all-ones Then, try: route add -host all-ones dev eth0 Another route that has worked for some users is: route add -net 255.255.255.0 dev eth0 If you are not using eth0 as your network interface, you should specify the network interface you *are* using in your route command. IP BOOTP AGENT Some versions of the Linux 2.1 kernel apparently prevent dhcpd from working unless you enable it by doing the following: echo 1 >/proc/sys/net/ipv4/ip_bootp_agent MULTIPLE INTERFACES Most older versions of the Linux kernel do not provide a networking API that allows dhcpd to operate correctly if the system has more than one broadcast network interface. However, Linux 2.0 kernels with version numbers greater than or equal to 2.0.31 add an API feature: the SO_BINDTODEVICE socket option. If SO_BINDTODEVICE is present, it is possible for dhcpd to operate on Linux with more than one network interface. In order to take advantage of this, you must be running a 2.0.31 or greater kernel, and you must have 2.0.31 system headers installed *before* you build dhcpd. NOTE: People have been having problems finding the 2.0.31 kernel because it was only available as a prerelease patch. As of October 17, Linux 2.0.31 is the stable Linux kernel, and is available as a kernel distribution rather than as a test patch. With any luck, it will be in the latest version of your favourite Linux distribution soon. If you are running a Linux 2.1 kernel, this does not guarantee that you have SO_BINDTODEVICE. Linux 2.0.31 was released quite a while after 2.1 kernel development began. The earliest Linux kernel in the 2.1 development stream with SO_BINDTODEVICE is version 2.1.68. We have heard reports that you must still add routes to 255.255.255.255 in order for the all-ones broadcast to work, even on 2.0.31 kernels. In fact, you now need to add a route for each interface. Hopefully the Linux kernel gurus will get this straight eventually. SCO SCO has the same problem as Linux (described earlier). The thing is, SCO *really* doesn't want to let you add a host route to the all-ones broadcast address. One technique that has been successful on some versions of SCO is the very bizarre command: ifconfig net0 alias 10.1.1.1 netmask 8.0.0.0 Apparently this works because of an interaction between SCO's support for network classes and the weird netmask. The 10.* network is just a dummy that can generally be assumed to be safe. Don't ask why this works. Just try it. If it works for you, great. If not, SCO is supposedly adding hooks to support real DHCP service in a future release - I have this on good authority from the people at SCO who do *their* DHCP server and client. HP-UX HP-UX has the same problem with the all-ones broadcast address that SCO and Linux have. One user reported that adding the following to /etc/rc.config.d/netconf helped (you may have to modify this to suit your local configuration): INTERFACE_NAME[0]=lan0 IP_ADDRESS[0]=1.1.1.1 SUBNET_MASK[0]=255.255.255.0 BROADCAST_ADDRESS[0]="255.255.255.255" LANCONFIG_ARGS[0]="ether" DHCP_ENABLE[0]=0 The above hack supposedly does not work on HP-UX version 9.x. However, another hack which supposedly _does_ work on 9.x is to add the following entry to your /etc/hosts or DNS database: 255.255.255.255 all-ones Then modify the broadcast as follows (change to suit your configuration, of course): ifconfig lan0 [your ip addr] netmask [your netmask] broadcast all-ones I would appreciate any reports as to how well this works for you. ULTRIX Now that we have Ultrix packet filter support, the DHCP Distribution on Ultrix should be pretty trouble-free. However, one thing you do need to be aware of is that it now requires that the pfilt device be configured into your kernel and present in /dev. If you type ``man packetfilter'', you will get some information on how to configure your kernel for the packet filter (if it isn't already) and how to make an entry for it in /dev. FreeBSD Versions of FreeBSD prior to 2.2 have a bug in BPF support in that the ethernet driver swaps the ethertype field in the ethernet header downstream from BPF, which corrupts the output packet. If you are running a version of FreeBSD prior to 2.2, and you find that dhcpd can't communicate with its clients, you should #define BROKEN_FREEBSD_BPF in site.h and recompile. NeXTSTEP The NeXTSTEP support uses the NeXTSTEP Berkeley Packet Filter extension, which is not included in the base NextStep system. You must install this extension in order to get dhcpd or dhclient to work. SUPPORT The Internet Software Consortium DHCP server is not a commercial product, and is not supported in that sense. However, it has attracted a fairly sizable following on the Internet, which means that there are a lot of knowledgable users who may be able to help you if you get stuck. These people generally read the dhcp-server@fugue.com mailing list. If you are going to use dhcpd, you should probably subscribe to the dhcp-server and dhcp-announce mailing lists. If you will be using dhclient, you should subscribe to the dhcp-client mailing list. PLEASE DO NOT send queries about non-isc clients to the dhcp-client mailing list. If you're asking about them on an ISC mailing list, it's probably because you're using the ISC DHCP server, so ask there. Please see http://www.fugue.com/dhcp/lists for details on how to subscribe. If you don't have WorldWide Web access, you can send mail to dhcp-request@fugue.com and tell me which lists you want to subscribe to, but please use the web interface if you can, since I have to handle the -request mailing list manually, and I will give you the third degree if you make me do your subscription manually. PLEASE DO NOT SEND REQUESTS FOR SUPPORT DIRECTLY TO ME! The number of people using the DHCP Distribution is sufficiently large that if I take an interrupt every time any one of those people runs into trouble, I will never get any more coding done. PLEASE DO NOT CALL ME ON THE PHONE FOR SUPPORT! Answering the phone takes a lot more of my time and attention than answering email. If you do call me on the phone, I will tell you to send email to the mailing list, and I won't answer your question, so there's no point in doing it. BUGS This release of the DHCP Distribution does not yet contain support for DHCPINFORM. Support for DHCPINFORM will be present in the release at a later time. DHCPINFORM is somewhat tangential to the main purpose of the DHCP protocol, so this probably won't be a major problem for most users. Vendor tags and User tags are not currently supported.