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		     Internet Software Consortium
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	   Dynamic Host Configuration Protocol Distribution
			 Engineering Release
			     May 8, 1997

This is an engineering 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.   This is a release of work in progress, and
should *not* be considered stable.   If it works for you, great.   If
not, let me know about the problem, but don't expect an immediate fix.
DHCP server users running a production environment should probably 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 network
interface is being used.  They also runs on QNX and Linux as long as
only one network interface is present and a host route is added from
that interface to the broadcast address.

The DHCP client currently only configures the network when running on
NetBSD.   This is because the client depends on a system-dependent
shell script to do network configuration, and the only such script
that currently exists in a distributable form is the one for NetBSD.
A version for Linux is under development.   For other operating
systems, you would have to develop your own.

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.

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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''.

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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.


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There are two big LINUX issues: the all-ones broadcast address, and
operations with more than one  network interface.


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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  Unfortunately, Linux insists on changing into the local subnet broadcast address (here, that's  This results in a DHCP protocol violation, and while
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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.
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It is possible to work around this problem on some versions of Linux
by creating a host route from your network interface address to   The command you need to use to do this on Linux
varies from version to version.   The easiest version is:
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	route add -host dev eth0
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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:
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84	all-ones
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Then, try:
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	route add -host all-ones dev eth0
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Another route that has worked for some users is:
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	route add -net dev eth0
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If you are not using eth0 as your network interface, you should
specify the network interface you *are* using in your route command.
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                        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 2.0.30 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.   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.

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.   I do not know what version of Linux 2.1 has
this feature.   To find out if yours does, check /usr/include/sys/sock*.h
to see if SO_BINDTODEVICE is defined.

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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:
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	ifconfig net0 alias netmask
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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.
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HP-UX has the same problem with the all-ones broadcast address that
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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):

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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.
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ISC DHCPD 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
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the 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.  For
details, please see  If you don't
have WorldWide Web access, you can send mail to
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.

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.

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
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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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Vendor tags and User tags are not currently supported.
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