Internet Systems Consortium DHCP Distribution Version 4.4.2 22 January 2020 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 ATF 6 SUPPORT 6.1 HOW TO REPORT BUGS 7 HISTORY 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 listed in the References document that is available in html, txt and xml formats in 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.example. 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. KEA Migration Assistant documentation, including how to build, install and use it, is including in the keama directory. 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. Please note that the pathnames of files to which our manpages refer will not be correct for your operating system until after you iterate 'make install' (so if you're reading a manpage out of the source directory, it may not have up-to-date information). 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: gunzip dhcp-4.4.2.tar.gz tar xvf dhcp-4.4.2.tar CONFIGURING IT Now, cd to the dhcp-4.4.2 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. Several options may be enabled or disabled via the configure command. You can get a list of these by typing: ./configure --help If you want to use dynamic shared libraries automake, autoconf (aka GNU autotools) and libtool must be available. The DHCP distribution provides 3 configure.ac* files: the -lt version has no libtool support and was copied to the configure.ac standard file in the distribution. To enable libtool support you should perform these steps: cp configure.ac+lt configure.ac autoreconf -i after you can use the regenerated configure as usual (with libtool support (--enable-libtool) on by default): ./configure For compatibility (and people who don't read this documentation) the --enable-libtool configuration file is supported even by the distributed configure (and off by default). The previous steps are performed and the regenerated configure called with almost the same parameters (this "almost" makes the use of this feature not recommended). Note you can't go back from with libtool support to without libtool support by restoring configure.ac and rerun autoreconf. If you want or need to restore the without libtool support state the required way is to simply restore the whole distribution. DYNAMIC DNS UPDATES A fully-featured implementation of dynamic DNS updates is included in this release. It uses libraries from BIND and, to avoid issues with different versions, includes the necessary BIND version. The appropriate BIND libraries will be compiled and installed in the bind subdirectory as part of the make step. In order to build the necessary libraries you will need to have "gmake" available on your build system. 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. If you cross compile you have to follow the instructions from the BIND README, in particular you must set the BUILD_CC environment variable. 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: PROTOCOL NOT CONFIGURED 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, or to select a kernel provided by your Linux distribution that has these enabled (virtually all modern ones do by default). 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 version 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 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. 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. LINUX: OpenWrt DHCP 4.1 has been tested on OpenWrt 7.09 and 8.09. In keeping with standard practice, client/scripts now includes a dhclient-script file for OpenWrt. However, this is not sufficient by itself to run dhcp on OpenWrt; a full OpenWrt package for DHCP is available at ftp://ftp.isc.org/isc/dhcp/dhcp-4.1.0-openwrt.tar.gz LINUX: 802.1q VLAN INTERFACES If you're using 802.1q vlan interfaces on Linux, it is necessary to vconfig the subinterface(s) to rewrite the 802.1q information out of packets received by the dhcpd daemon via LPF: vconfig set_flag eth1.523 1 1 Note that this may affect the performance of your system, since the Linux kernel must rewrite packets received via this interface. For more information, consult the vconfig man pages. ATF Please see the file DHCP/doc/devel/atf.dox for a description of building and using these tools. The optional unit tests use ATF (Automated Testing Framework) including the atf-run and atf-report tools. ATF deprecated these tools in version 0.19 and removed these tools from its sources in version 0.20, requiring you to get an older version, use Kyua with an ATF compatibility package or use the version included in the Bind sources. SUPPORT The Internet Systems Consortium DHCP server is developed and distributed by ISC in the public trust, thanks to the generous donations of its sponsors. ISC now also offers commercial quality support contracts for ISC DHCP, more information about ISC Support Contracts can be found at the following URL: https://www.isc.org/support/ Please understand that we may not respond to support inquiries unless you have a support contract. ISC will continue its practice of always responding to critical items that effect the entire community, and responding to all other requests for support upon ISC's mailing lists on a best-effort basis. However, ISC DHCP has attracted a fairly sizable following on the Internet, which means that there are a lot of knowledgeable users who may be able to help you if you get stuck. These people generally read the dhcp-users@isc.org mailing list. Be sure to provide as much detail in your query as possible. If you are going to use ISC DHCP, you should probably subscribe to the dhcp-users or dhcp-announce mailing lists. WHERE TO SEND FEATURE REQUESTS: We like to hear your feedback. We may not respond to it all the time, but we do read it. If ISC DHCP doesn't work well for you, or you have an idea that would improve it for your use, please create an issue at https://gitlab.isc.org/isc-projects/dhcp/issues. This is also an excellent place to send patches that add new features. WHERE TO REPORT BUGS: If you want the act of sending in a bug report to result in you getting help in the form of a fixed piece of software, you are asking for help. Your bug report is helpful to us, but fundamentally you are making a support request, so please use the addresses described in the previous paragraphs. If you are _sure_ that your problem is a bug, and not user error, or if your bug report includes a patch, you can submit it to our ticketing system at https://gitlab.isc.org/isc-projects/dhcp/issues. If you have not received a notice that the ticket has been resolved, then we're still working on it. PLEASE DO NOT REPORT BUGS IN OLD SOFTWARE RELEASES! Fetch the latest release and see if the bug is still in that version of the software, and if it is still present, _then_ report it. ISC release versions always have three numbers, for example: 1.2.3. The 'major release' is 1 here, the 'minor release' is 2, and the 'maintenance release' is 3. ISC will accept bug reports against the most recent two major.minor releases: for example, 1.0.0 and 0.9.0, but not 0.8.* or prior. PLEASE take a moment to determine where the ISC DHCP distribution that you're using came from. ISC DHCP is sometimes heavily modified by integrators in various operating systems - it's not that we feel that our software is perfect and incapable of having bugs, but rather that it is very frustrating to find out after many days trying to help someone that the sources you're looking at aren't what they're running. When in doubt, please retrieve the source distribution from ISC's web page and install it. HOW TO REPORT BUGS OR REQUEST HELP When you report bugs or ask for help, 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. This will save us a great deal of time and more informative bug reports are more likely to get handled more quickly overall. 1. The specific operating system name and version of the machine on which the DHCP server or client is running. 2. 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. 3. 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 trying. 4. The specific version of the DHCP distribution you're running, as reported by dhcpd -t. 5. 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. 6. Include your dhcpd.conf and dhcpd.leases file as MIME attachments if they're not over 100 kilobytes in size each. If they are this large, please make them available to us, e.g., via a hidden http:// URL or FTP site. If you're not comfortable releasing this information due to sensitive contents, you may encrypt the file to our release signing key, available on our website. 7. 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. 8. 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 following: gdb dhcpd dhcpd.core (gdb) where [...] (gdb) quit This assumes that it's the dhcp server you're debugging, and that the core file is in dhcpd.core. Please see https://www.isc.org/dhcp/ for details on how to subscribe to the ISC DHCP mailing lists. HISTORY ISC DHCP was originally written by Ted Lemon under a contract with Vixie Labs with the goal of being a complete reference implementation of the DHCP protocol. Funding for this project was provided by Internet Systems Consortium. The first release of the ISC DHCP distribution in December 1997 included just the DHCP server. Release 2 in June 1999 added a DHCP client and a BOOTP/DHCP relay agent. DHCP 3 was released in October 2001 and included DHCP failover support, OMAPI, Dynamic DNS, conditional behaviour, client classing, and more. Version 3 of the DHCP server was funded by Nominum, Inc. The 4.0 release in December 2007 introduced DHCPv6 protocol support for the server and client. This product includes cryptographic software written by Eric Young (eay@cryptsoft.com).