readme

DHCP服务器源码

	       Internet Systems Consortium DHCP Distribution
			     Version 3.0.1
			     July 14, 2004

			      README FILE

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
	 3.1	 UNPACKING IT
	 3.2	 CONFIGURING IT
	  3.2.1	  DYNAMIC DNS UPDATES
	  3.2.2   LOCALLY DEFINED OPTIONS
	 3.3	 BUILDING IT
	4	INSTALLING THE DHCP DISTRIBUTION
	5	USING THE DHCP DISTRIBUTION
	 5.1	  FIREWALL RULES
	 5.2	 LINUX
	  5.2.1	  IF_TR.H NOT FOUND
	  5.2.2	  SO_ATTACH_FILTER UNDECLARED
	  5.2.3	  PROTOCOL NOT CONFIGURED
	  5.2.4	  BROADCAST
	  5.2.6	  IP BOOTP AGENT
	  5.2.7	  MULTIPLE INTERFACES
	 5.3	 SCO
	 5.4	 HP-UX
	 5.5	 ULTRIX
	 5.6	 FreeBSD
	 5.7	 NeXTSTEP
	 5.8	 SOLARIS
	6	SUPPORT
	 6.1	 HOW TO REPORT 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.  The README file (this file) includes
late-breaking operational and system-specific information that you
should read even if you don't want to read the manual pages, and that
you should *certainly* read if you run into trouble.  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
DHCP Distribution.

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
system.

			    RELEASE STATUS

This is release version 3.0.1 of the ISC DHCP Distribution.  

In this release, the server and relay agent are currently fully
functional on NetBSD, Linux systems with kernel version 2.2 or later,
FreeBSD, OpenBSD, BSD/OS, Digital Tru64 Unix and Solaris.  The software
will also run on HP-UX, but only supports a single network interface.
Ports also exist for QNX, SCO, NeXTStep, and MacOS X, but are not in
wide use, with all that implies.   We are not aware of an easy way to
get this software running on HP-UX.

The DHCP client currently only knows how to configure the network on
NetBSD, FreeBSD, OpenBSD, 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 are running the DHCP distribution on a machine which is a
firewall, or if there is a firewall between your DHCP server(s) and
DHCP clients, please read the section on firewalls which appears later
in this document.

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

			     UNPACKING IT

To build the DHCP Distribution, unpack the compressed tar file using
the tar utility and the gzip command - type something like:

	zcat dhcp-3.0.1.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.

			    CONFIGURING IT

Now, cd to the dhcp-3.0.1 subdirectory that you've just created and
configure the source tree by typing:

	./configure

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
your own.

			 DYNAMIC DNS UPDATES

A fully-featured implementation of dynamic DNS updates is included in
this release.   There are no build dependencies with any BIND version
- this version can and should just use the resolver in your C library.

There is documentation for the DDNS support in the dhcpd.conf manual
page - see the beginning of this document for information on finding
manual pages.

		       LOCALLY DEFINED OPTIONS

In previous versions of the DHCP server there was a mechanism whereby
options that were not known by the server could be configured using
a name made up of the option code number and an identifier:
"option-nnn"   This is no longer supported, because it is not future-
proof.   Instead, if you want to use an option that the server doesn't
know about, you must explicitly define it using the method described
in the dhcp-options man page under the DEFINING NEW OPTIONS heading.

			     BUILDING IT

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
Distribution working.

		   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

			    FIREWALL RULES

If you are running the DHCP server or client on a computer that's also
acting as a firewall, you must be sure to allow DHCP packets through
the firewall.  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.

We have noticed that on some systems where we are using a packet
filter, if you set up a firewall that blocks UDP port 67 and 68
entirely, packets sent through the packet filter will not be blocked.
However, unicast packets will be blocked.   This can result in strange
behaviour, particularly on DHCP clients, where the initial packet
exchange is broadcast, but renewals are unicast - the client will
appear to be unable to renew until it starts broadcasting its
renewals, and then suddenly it'll work.   The fix is to fix the
firewall rules as described above.

			   PARTIAL SERVERS

If you have a server that is connected to two networks, and you only
want to provide DHCP service on one of those networks (e.g., you are
using a cable modem and have set up a NAT router), if you don't write
any subnet declaration for the network you aren't supporting, the DHCP
server will ignore input on that network interface if it can.  If it
can't, it will refuse to run - some operating systems do not have the
capability of supporting DHCP on machines with more than one
interface, and ironically this is the case even if you don't want to
provide DHCP service on one of those interfaces.

				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.   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:

 Make sure CONFIG_PACKET (Packet socket) and CONFIG_FILTER (Socket
 Filtering) are enabled in your kernel configuration

If this happens, you need to configure your Linux kernel to support
Socket Filtering and the Packet socket.  You can do this by typing
``make config'', ``make menuconfig'' or ``make xconfig'', and then
enabling the Packet socket and Socket Filtering options that you'll
see displayed on the menu or in the questionnaire.  You can also edit
your linux kernel .config file directly: set CONFIG_FILTER=y and
CONFIG_PACKET=y.  If you do this, make sure you run ``make oldconfig''
afterwards, so that the changes you've made are propogated to the
kernel header files.   After you've reconfigured, you need to type
``make'' to build a new Linux kernel, and then install it in the
appropriate place (probably /linux).  Make sure to save a copy of your
old /linux.

If the preceding paragraph 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
kernel issue.   This is probably not a problem with the most recent
Linux 2.2.x kernels.

			   LINUX: BROADCAST

If you are running a recent version of Linux, this won't be a problem,
but on older versions of Linux (kernel versions prior to 2.2), there
is a potential problem with the broadcast address being sent
incorrectly.

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 changes an IP
destination of 255.255.255.255 into the local subnet broadcast address
(here, that's 192.5.5.223).

This isn't generally a problem on Linux 2.2 and later kernels, since
we completely bypass the Linux IP stack, but on old versions of Linux
2.1 and all versions of Linux prior to 2.1, it is a problem - pickier
DHCP clients connected to the same network as the ISC DHCP server or
ISC relay agent will not see messages from the DHCP server.   It *is*
possible to run into trouble with this on Linux 2.2 and later if you
are running a verson of the DHCP server that was compiled on a Linux
2.0 system, though.

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