Internet Software Consortium
Dynamic Host Configuration Protocol Distribution
June 22, 1999
You should read this file carefully before trying to install or use
the ISC DHCP Distribution.
TABLE OF CONTENTS
1 WHERE TO FIND DOCUMENTATION
2 RELEASE STATUS
3 BUILDING THE DHCP DISTRIBUTION
4 INSTALLING THE DHCP DISTRIBUTION
5 USING THE DHCP DISTRIBUTION
5.1.1 SO_ATTACH_FILTER UNDECLARED
5.1.2 PROTOCOL NOT CONFIGURED
5.1.4 FIREWALL RULES
5.1.5 IP BOOTP AGENT
5.1.6 MULTIPLE INTERFACES
6.1 HOW TO REPORT BUGS
7 KNOWN BUGS
WHERE TO FIND DOCUMENTATION
Documentation for this software includes this README file, the
RELNOTES file, and the manual pages, which are in the server, common,
client and relay subdirectories. Internet standards relating to the
DHCP protocol are stored in the doc subdirectory. You will have the
best luck reading the manual pages if you build this software and then
install it, although you can read them directly out of the
distribution if you need to.
DHCP server documentation is in the dhcpd man page. Information about
the DHCP server lease database is in the dhcpd.leases man page.
Server configuration documentation is in the dhcpd.conf man page as
well as the dhcp-options man page. A sample DHCP server
configuration is in the file server/dhcpd.conf. The source for the
dhcpd, dhcpd.leases and dhcpd.conf man pages is in the server/ sub-
directory in the distribution. The source for the dhcp-options.5
man page is in the common/ subdirectory.
DHCP Client documentation is in the dhclient man page. DHCP client
configuration documentation is in the dhclient.conf man page and the
dhcp-options man page. The DHCP client configuration script is
documented in the dhclient-script man page. The format of the DHCP
client lease database is documented in the dhclient.leases man page.
The source for all these man pages is in the client/ subdirectory in
the distribution. In addition, the dhcp-options man page should be
referred to for information about DHCP options.
DHCP relay agent documentation is in the dhcrelay man page, the source
for which is distributed in the relay/ subdirectory.
To read installed manual pages, use the man command. Type "man page"
where page is the name of the manual page. This will only work if
you have installed the ISC DHCP distribution using the ``make install''
command (described later).
If you want to read manual pages that aren't installed, you can type
``nroff -man page |more'' where page is the filename of the
unformatted manual page. The filename of an unformatted manual page
is the name of the manual page, followed by '.', followed by some
number - 5 for documentation about files, and 8 for documentation
about programs. For example, to read the dhcp-options man page,
you would type ``nroff -man common/dhcp-options.5 |more'', assuming
your current working directory is the top level directory of the ISC
If you do not have the nroff command, you can type ``more catpage''
where catpage is the filename of the catted man page. Catted man
pages names are the name of the manual page followed by ".cat"
followed by 5 or 8, as with unformatted manual pages.
Please note that until you install the manual pages, the pathnames of
files to which they refer will not be correct for your operating
This is the final 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 release is stable.
In this release, the server and relay agent currently work well on
NetBSD, Linux after kernel version 2.0.30, FreeBSD, BSD/OS, Ultrix,
Digital Alpha OSF/1, Solaris and SunOS 4.1.4. On AIX, HPUX, IRIX and
Linux 2.0.30, only a single broadcast network interface is supported.
They also runs on QNX 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.
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 an
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, unpack the compressed tar file using
the tar utility and the gzip command - type something like:
zcat dhcp-2.0b1pl29.tar.gz |tar xvf -
On BSD/OS, you have to type gzcat, not zcat, and you may run into
similar problems on other operating systems.
Now, cd to the dhcp-2.0b1pl29 subdirectory that you've just created and
configure the source tree by typing:
If the configure utility 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
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 warnings, it's not likely to be a problem - the DHCP
server compiles completely warning-free on as many architectures
as we can manage, but there are a few for which this is difficult.
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
INSTALLING THE DHCP DISTRIBUTION
Once you have successfully gotten the DHCP Distribution to build, you
can install it by typing ``make install''. If you already have an old
version of the DHCP Distribution installed, you may want to save it
before typing ``make install''.
USING THE DHCP DISTRIBUTION
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. There are also two potential compilation/runtime
problems for Linux 2.1/2.2: the "SO_ATTACH_FILTER undeclared" problem
and the "protocol not configured" problem.
LINUX: SO_ATTACH_FILTER UNDECLARED
In addition, there is a minor issue that we will mention here because
this release is so close on the heels of the Linux 2.2 release: there
is a symlink in /usr/include that points at the linux asm headers. It
appears to be not uncommon that this link won't be updated correctly,
in which case you'll get the following error when you try to build:
lpf.c: In function `if_register_receive':
lpf.c:152: `SO_ATTACH_FILTER' undeclared (first use this function)
lpf.c:152: (Each undeclared identifier is reported only once
lpf.c:152: for each function it appears in.)
The line numbers may be different, of course. If you see this
header, your linux asm header link is probably bad, and you should
make sure it's pointing to correct linux source directory.
LINUX: PROTOCOL NOT CONFIGURED
One additional Linux 2.1/2.2 issue: if you get the following message,
it's because your kernel doesn't have the linux packetfilter or raw
packet socket configured:
Set CONFIG_PACKET=y and CONFIG_FILTER=y in your kernel configuration
If this happens, you need to edit your linux kernel .config file, set
CONFIG_FILTER=y and CONFIG_PACKET=y, and rebuild your kernel. If the
preceding sentence made no sense to you, ask your Linux vendor/guru
for help - please don't ask us.
If you set CONFIG_PACKET=m or CONFIG_FILTER=m, then you must tell the
kernel module loader to load the appropriate modules. If this doesn't
make sense to you, don't use CONFIG_whatever=m - use CONFIG_whatever=y.
Don't ask for help with this on the DHCP mailing list - it's a Linux
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
220.127.116.11). 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
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.
LINUX: FIREWALL RULES
If you are running the DHCP server or client on a Linux system that's
also acting as a firewall, you must be sure to allow DHCP packets
through the firewall - Linux firewalls make filtering decisions before
they make the forwarding decision, so they will filter packets that
are intended for the firewall itself, as well as packets intended to
be forwarded. In particular, your firewall rules _must_ allow
packets from IP address 0.0.0.0 to IP address 255.255.255.255 from UDP
port 68 to UDP port 67 through. They must also allow packets from
your local firewall's IP address and UDP port 67 through to any
address your DHCP server might serve on UDP port 68. Finally,
packets from relay agents on port 67 to the DHCP server on port 67,
and vice versa, must be permitted.
LINUX: 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
LINUX: MULTIPLE INTERFACES
Very old 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 or later system
headers installed *before* you build the DHCP Distribution.
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.
Linux 2.1 and later kernels do not use SO_BINDTODEVICE or require the
broadcast address hack, but do support multiple interfaces, using the
Linux Packet Filter.
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 18.104.22.168
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 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):
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.
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.
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.
One problem which has been observed and is not fixed in this
patchlevel has to do with using DLPI on Solaris machines. The symptom
of this problem is that the DHCP server never receives any requests.
If you are using Solaris 2.6, and you encounter this symptom, and
you are running the DHCP server on a machine with a single broadcast
network interface, you may wish to edit the includes/site.h file and
uncomment the #define USE_SOCKETS line. Then type ``make clean;
The DHCP client on Solaris will only work with DLPI. If you run it
and it just keeps saying it's sending DHCPREQUEST packets, but never
gets a response, you may be having DLPI trouble as described above.
If so, you are SOL. Also, because Solaris requires you to "plumb" an
interface before it can be detected by the DHCP client, you must
either specify the name(s) of the interface(s) you want to configure
on the command line, or must plumb the interfaces prior to invoking
the DHCP client. This can be done with ``ifconfig iface plumb'',
where iface is the name of the interface (e.g., ``ifconfig hme0
It should be noted that Solaris versions from 2.6 onward include a
DHCP client that you can run with ``/sbin/ifconfig iface dhcp start''
rather than using the ISC DHCP client. The feature set of the Solaris
client is different (not necessarily better or worse) than that of the
ISC client, but in most cases it will be a lot easier for you to just
use that. Please do not ask for help in using the Solaris DHCP client
on Internet Software Consortium mailing lists - that's why you're
paying Sun the big bucks. If you're having a problem with the
Solaris client interoperating with the ISC dhcp server, that's another
matter, but please check with Sun first.
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 firstname.lastname@example.org
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.
If you need help, you should ask on the dhcp-server or dhcp-client
mailing list (or both) - whichever is appropriate to your
application. This includes reporting bugs. Please do not report
bugs in old software releases - fetch the latest release and see if
the bug is still in that copy of the software, and if it's not, _then_
report it. It's okay to report bugs in the latest patchlevel of a
major version that's not the most recent major version, though - for
example, if you're running 2.0, you don't have to upgrade to 3.0
before you can report bugs.
PLEASE READ THIS README FILE CAREFULLY BEFORE REPORTING BUGS!
HOW TO REPORT BUGS
When you report bugs, please provide us complete information. A list
of information we need follows. Please read it carefully, and put
all the information you can into your initial bug report, so that we
don't have to ask you any questions in order to figure out your
- The specific operating system name and version of the
machine on which the DHCP server or client is running.
- The specific operating system name and version of the
machine on which the client is running, if you are having
trouble getting a client working with the server.
- If you're running Linux, the version number we care about is
the kernel version and maybe the library version, not the
distribution version - e.g., while we don't mind knowing
that you're running Redhat version mumble.foo, we must know
what kernel version you're running, and it helps if you can
tell us what version of the C library you're running,
although if you don't know that off the top of your head it
may be hard for you to figure it out, so don't go crazy
- The specific version of the DHCP distribution you're
running, for example 2.0b1pl19, not 2.0.
- Please explain the problem carefully, thinking through what
you're saying to ensure that you don't assume we know
something about your situation that we don't know.
- Include your dhcpd.conf and dhcpd.leases file if they're not
huge (if they are huge, we may need them anyway, but don't
send them until you're asked).
- Include a log of your server or client running until it
encounters the problem - for example, if you are having
trouble getting some client to get an address, restart the
server with the -d flag and then restart the client, and
send us what the server prints. Likewise, with the client,
include the output of the client as it fails to get an
address or otherwise does the wrong thing. Do not leave
out parts of the output that you think aren't interesting.
- If the client or server is dumping core, please run the
debugger and get a stack trace, and include that in your
bug report. For example, if your debugger is gdb, do the
gdb dhcpd dhcpd.core
This assumes that it's the dhcp server you're debugging, and
that the core file is in dhcpd.core.
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.
If you are having problems with a client whose executable is called
dhcpcd, this is _not_ the ISC DHCP client, and we probably can't help
you with it.
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 email@example.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
This release of the DHCP Distribution does not yet contain support for
DHCPINFORM. The Vendor Specific Data option is not supported. Site-
specific options are not supported. All of these are supported in the
3.0 release of the DHCP distribution, which is now in beta testing.