Multihomed pc

[Simon Hobson]

Crisfalusi Dan wrote:

>I have pc's that move from time to time in a relative large network 
>(with tens of routers).
>In the network they all receive their IP address from a central dhcp server.

All normal stuff

>For security reasons all pc's have a fix mac-ip association.

REPEAT AFTER ME - DHCP DOES NOT OFFER SECURITY. You may get an 
illusion of security, but there really is NO security in dhcp - it 
CANNOT prevent someone simply copying the network settings from 
another device and using them.

>My problem is that I don't know how to change the association of 
>mac-ip from dhcpd.conf file
>automatically not by hand (using some match and if statements), 
>based on giaddr (the IP of the first entry router).

You do not need match statements etc, it is handled automagically by 
the dhcp server. Simply define multiple IP addresses for the client, 
eg :

host pc1 {
   hardware ethernet aa:bb:cc:dd:ee:ff ;
   fixed address 192.168.1.17, 192.168.57.21, 172.20.15.93 ;
}