Internet Software Consortium
Dynamic Host Configuration Protocol Distribution
Version 2, Beta 1, Patchlevel 0
December 6, 1997
This is the first Beta release of Version 2 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.
This beta is believed to be fairly stable. However, DHCP server users
running a production environment should probably still use version
1.0, 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
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.
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