158 lines
6.5 KiB
Plaintext
158 lines
6.5 KiB
Plaintext
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LDAP Support in DHCP
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Brian Masney <masneyb@ntelos.net>
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Last updated 8/16/2002
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This document describes setting up the DHCP server to read it's configuration
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from LDAP. This work is based on the IETF document
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draft-ietf-dhc-ldap-schema-01.txt included in the doc directory. For the latest
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version of this document, please see http://home.ntelos.net/~masneyb.
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First question on most people's mind is "Why do I want to store my
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configuration in LDAP?" If you run a small DHCP server, and the configuration
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on it rarely changes, then you won't need to store your configuration in LDAP.
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But, if you have several DHCP servers, and you want an easy way to manage your
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configuration, this can be a solution.
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The first step will be to setup your LDAP server. I am using OpenLDAP from
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www.openldap.org. Building and installing OpenLDAP is beyond the scope of this
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document. There is plenty of documentation out there about this. Once you have
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OpenLDAP installed, you will have to edit your slapd.conf file. I added the
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following 2 lines to my configuration file:
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include /etc/ldap/schema/dhcp.schema
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index dhcpHWAddress eq
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index dhcpClassData eq
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The first line tells it to include the dhcp schema file. You will find this
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file under the contrib directory in this distribution. You will need to copy
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this file to where your other schema files are (maybe
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/usr/local/openldap/etc/openldap/schema/). The second line sets up
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an index for the dhcpHWAddress parameter. The third parameter is for reading
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subclasses from LDAP every time a DHCP request comes in. Make sure you run the
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slapindex command and restart slapd to have these changes to into effect.
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Now that you have LDAP setup, you should be able to use gq (http://biot.com/gq/)
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to verify that the dhcp schema file is loaded into LDAP. Pull up gq, and click
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on the Schema tab. Go under objectClasses, and you should see at least the
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following object classes listed: dhcpClass, dhcpGroup, dhcpHost, dhcpOptions,
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dhcpPool, dhcpServer, dhcpService, dhcpSharedNetwork, dhcpSubClass, and
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dhcpSubnet. If you do not see these, you need to check over your LDAP
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configuration before you go any further.
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You should be ready to build DHCP. Edit the includes/site.h file and uncomment
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the #define LDAP_CONFIGURATION. Now run configure in the base source directory.
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Edit the work.os/server/Makefile and add -lldap to the LIBS= line. (replace os
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with your operating system, linux-2.2 on my machine). You should be able to
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type make to build your DHCP server.
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Once you have DHCP installed, you will need to setup your initial plaintext
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config file. In my /etc/dhcpd.conf file, I have:
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ldap-server "localhost";
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ldap-port 389;
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ldap-username "cn=DHCP User, dc=ntelos, dc=net";
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ldap-password "blah";
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ldap-base-dn "dc=ntelos, dc=net";
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ldap-method dynamic;
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All of these parameters should be self explanatory except for the ldap-method.
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You can set this to static or dynamic. If you set it to static, the
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configuration is read once on startup, and LDAP isn't used anymore. But, if you
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set this to dynamic, the configuration is read once on startup, and the
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hosts that are stored in LDAP are looked up every time a DHCP request comes in.
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The next step is to set up your LDAP tree. Here is an example config that will
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give a 10.100.0.x address to machines that have a host entry in LDAP.
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Otherwise, it will give a 10.200.0.x address to them. (NOTE: replace
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dc=ntelos, dc=net with your base dn). If you would like to convert your
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existing dhcpd.conf file to LDIF format, there is a script
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contrib/dhcpd-conf-to-ldap.pl that will convert it for you.
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# You must specify the server's host name in LDAP that you are going to run
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# DHCP on and point it to which config tree you want to use. Whenever DHCP
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# first starts up, it will do a search for this entry to find out which
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# config to use
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dn: cn=brian.ntelos.net, dc=ntelos, dc=net
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objectClass: top
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objectClass: dhcpServer
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cn: brian.ntelos.net
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dhcpServiceDN: cn=DHCP Service Config, dc=ntelos, dc=net
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# Here is the config tree that brian.ntelos.net points to.
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dn: cn=DHCP Service Config, dc=ntelos, dc=net
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cn: DHCP Service Config
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objectClass: top
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objectClass: dhcpService
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dhcpPrimaryDN: dc=ntelos, dc=net
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dhcpStatements: ddns-update-style ad-hoc
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dhcpStatements: default-lease-time 600
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dhcpStatements: max-lease-time 7200
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# Set up a shared network segment
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dn: cn=WV Test, cn=DHCP Service Config, dc=ntelos, dc=net
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cn: WV
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objectClass: top
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objectClass: dhcpSharedNetwork
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# Set up a subnet declaration with a pool statement. Also note that we have
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# a dhcpOptions object with this entry
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dn: cn=10.100.0.0, cn=WV Test, cn=DHCP Service Config, dc=ntelos, dc=net
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cn: 10.100.0.0
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objectClass: top
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objectClass: dhcpSubnet
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objectClass: dhcpOptions
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dhcpOption: domain-name-servers 10.100.0.2
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dhcpOption: routers 10.100.0.1
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dhcpOption: subnet-mask 255.255.255.0
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dhcpOption: broadcast-address 10.100.0.255
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dhcpNetMask: 24
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# Set up a pool for this subnet. Only known hosts will get these IPs
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dn: cn=Known Pool, cn=10.100.0.0, cn=WV Test, cn=DHCP Service Config, dc=ntelos, dc=net
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cn: Known Pool
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objectClass: top
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objectClass: dhcpPool
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dhcpRange: 10.100.0.3 10.100.0.254
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dhcpPermitList: deny unknown-clients
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# Set up another subnet declaration with a pool statement
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dn: cn=10.200.0.0, cn=WV Test, cn=DHCP Service Config, dc=ntelos, dc=net
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cn: 10.200.0.0
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objectClass: top
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objectClass: dhcpSubnet
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objectClass: dhcpOptions
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dhcpOption: domain-name-servers 10.200.0.2
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dhcpOption: routers 10.200.0.1
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dhcpOption: subnet-mask 255.255.255.0
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dhcpOption: broadcast-address 10.200.0.255
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dhcpNetMask: 24
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# Set up a pool for this subnet. Only unknown hosts will get these IPs
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dn: cn=Known Pool, cn=10.200.0.0, cn=WV Test, cn=DHCP Service Config, dc=ntelos, dc=net
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cn: Known Pool
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objectClass: top
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objectClass: dhcpPool
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dhcpRange: 10.200.0.3 10.200.0.254
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dhcpPermitList: deny known clients
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# Set aside a group for all of our known MAC addresses
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dn: cn=Customers, cn=DHCP Service Config, dc=ntelos, dc=net
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objectClass: top
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objectClass: dhcpGroup
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cn: Customers
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# Host entry for my laptop
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dn: cn=brianlaptop, cn=Customers, cn=DHCP Service Config, dc=ntelos, dc=net
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objectClass: top
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objectClass: dhcpHost
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cn: brianlaptop
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dhcpHWAddress: ethernet 00:00:00:00:00:00
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You can use the command slapadd to load all of these entries into your LDAP
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server. After you load this, you should be able to start up DHCP. If you run
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into problems reading the configuration, try running dhcpd with the -d flag.
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If you still have problems, edit the site.conf file in the DHCP source and
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add the line: COPTS= -DDEBUG_LDAP and recompile DHCP. (make sure you run make
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clean and rerun configure before you rebuild).
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