DHCP

Revision as of 10:17, 23 January 2007

DHCP

Dynamic Host Configuration Protocol. DHCP allows you to place machines on a network and configure many of their settings (network-wise) via a server that your host machine queries. Usually this is limited to what IP and DNS client information a host uses on the network, and this greatly increases an administrator's ability to configure a large number of hosts to use a network with minimal effort (as opposed to configuring each host individually.)

The service daemon on most *nix platforms is called dhcpd, the client application (if your *nix box is set up to use DHCP,) is usually dhclient.

Software

The most common unix implementation of the DHCP service is the ISC's DHCP; Microsoft has their own implementation, as does Sun Microsystems.

Configuration

(placeholder...needs info on hosts, networks, shared-networks and the different options)

DHCP - Install and setup

Server setup.

install through package

# pkg_add -r isc-dhcp3-server

We do this so we can define the root path for the diskless system.

copy /usr/local/etc/dhcpd.conf.sample to /usr/local/etc/dhcpd.conf

edit /usr/local/etc/dhcpd.conf and make sure it has these lines in it.

# dhcpd.conf
#
# Sample configuration file for ISC dhcpd
#

# option definitions common to all supported networks...
#option domain-name "example.org";
#option domain-name-servers ns1.example.org, ns2.example.org;

default-lease-time 3600;
max-lease-time 86400;

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
authoritative;

# ad-hoc DNS update scheme - set to "none" to disable dynamic DNS updates.
ddns-update-style none;

option root-path "192.168.1.1:/diskless_ro";

# lines added for pxeboot client
use-host-decl-names on;
next-server 192.168.1.1;
filename "pxeboot";

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;

# No service will be given on this subnet, but declaring it helps the
# DHCP server to understand the network topology.


# This is a very basic subnet declaration.

subnet 192.168.1.0 netmask 255.255.255.0 {
  range 192.168.1.10 192.168.1.20;
}

Create the leases file

# touch /var/db/dhcpd.leases

Restart the daemon

# killall dhcpd
# dhcpd

Add to /etc/rc.conf

dhcpd_enable="YES"

Problems starting dhcpd

Errors when trying to start

NOTE: This problem was found on this architecture, but may apply to others.

dhcp-1# uname -a
FreeBSD dhcp-1.one.example.com 6.0-RELEASE FreeBSD 6.0-RELEASE #0: Thu Nov  3 09:36:13 UTC 2005   
root@x64.samsco.home:/usr/obj/usr/src/sys/GENERIC  i386
dhcp-1#

dhcp-1# /usr/local/etc/rc.d/isc-dhcpd.sh start
chown: dhcpd: Invalid argument
/usr/local/etc/rc.d/isc-dhcpd.sh: WARNING: unable to change permissions of /var/run/dhcpd
/usr/local/etc/rc.d/isc-dhcpd.sh: WARNING: safe_run: chown dhcpd:dhcpd /var/db/dhcpd
/usr/local/etc/rc.d/isc-dhcpd.sh: WARNING: unable to change permissions of /var/db/dhcpd
chown: dhcpd: Invalid argument
/usr/local/etc/rc.d/isc-dhcpd.sh: WARNING: unable to change permissions of /var/db/dhcpd/dhcpd.leases
Starting dhcpd.
dhcp-1#

Find out if dhcpd is running

dhcp-1# ps -auwx | grep dhcp
root     94818  0.0  0.6  2188  1536  ??  Is   15Jan07   0:00.05 /usr/local/sbin/dhcpd
root     24289  0.0  1.1  3892  2612  p0  RV    6:22AM   0:00.00 grep dhcp (csh)

Stop dhcpd (if running)

dhcp-1# kill -9 94818

Verify that dhcpd has been stopped

dhcp-1# ps -auwx | grep dhcp
root     24293  0.0  0.1   348   208  p0  R+    6:22AM   0:00.00 grep dhcp

Fix the problem

dhcp-1# /usr/local/etc/rc.d/isc-dhcpd.sh install
Added group "dhcpd".
Added user "dhcpd".
dhcp-1# 

Start dhcpd normally

dhcp-1# /usr/local/etc/rc.d/isc-dhcpd.sh start
Starting dhcpd.
dhcp-1#