DHCP (Dynamic host configuration protocol)

DHCP allows client machines (eg macs, pcs and unix machines) to load their network information from a server. Thus certain network values (such as dns server etc) can be updated automatically from the server.

Our network defines all hosts statically (by their ethernet number) and a number of 'leased' IP numbers for new hosts.

Packages

Under linux, following rpm's are required (for mandrake8.0).

dhcp-2.0pl5-6mdk

Hosts

DHCP can run a number of serves on the same network so we shall define a number of dhcp servers for the department.

neo main server (100M esc network)
s2 (is really neo)
s3 backup server (100M its network connected)
s4 ACRC server (100M connected in building 27)
kali old piece of junk (100M esc network)
virtual exporer ACRC server (10M in building 27)
bifrost cam's server (100M esc network)

Files

/etc/dhcpd.conf
This is the configuration file that defines what hosts are known and which IP numbers are available.
/var/lib/dhcp/dhcpd.leases
This file keeps track of the leased ip numbers on the network.

The dhcpd.conf file is generated from the host/machine database and should not be edited by hand.

dhcpd.leases is managed by the server process on the host and can be used to track down new hosts (sometimes, pc's especially) as it sometimes contains 'host names'.

Configuration

No configuration is required as the host/machine database generates the conf file and that is all thats needed.

Problems...?

DHCP should be reasonably stable because of the redundancy. The host/machine database should restart the service when it updates the config file.

You must be root to do the following.

sh /etc/rc.d/init.d/dhcph status
sh /etc/rc.d/init.d/dhcpd stop
sh /etc/rc.d/init.d/dhcpd start

Finding unregistered machines

People just plug machines into our network and dont register them, so....

Looking in the lease file will tell you which numbers have been allocated to what ethernet addresses.

You can identify a host type with: nmap -O ipnumber while the host is active.

Checking the logs on orion (/var/adm/SYSLOG) might tell you who is using that dhcplease.