i would like to know if i have one interface with 2 or more ip address of diferent networks, can it be a DHCP server for the two or more networks it is conected to ?

I had configured it with only one ip address to only one network but i its not enough.

It should work but I've never had the need to configure multiple subnets. Just add another section.

subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.50 192.168.1.200;
}

subnet 192.168.2.0 netmask 255.255.255.0 {
range 192.168.2.50 192.168.2.200;
}

See man pages for additional help.
http://seth.positivism.org/man.cgi/8/dhcpd

The problem with that is it has no way to distinguish which hosts should belong to which network unless you specify all of the MAC addresses. If you are serving DHCP to multiple subnets out one interface then since DHCP requests are layer 2 and don't involve the IP address (yet, at least not the request itself) you will be randomly placing the clients on either network. This is of course assuming it is even possible to get DHCP to listen for two subnets on the same interface, which I have never had reason to try (due to the issue stated above) so do not know if it's possible.

Hi,

It seems to me that this could be interesting in 2 configurations :
1/ When using vlans... the dhcp requests would be in the one vlan or the other... so that should work.
2/ When forwarding dhcp request over a layer 3 network : I know that Cisco routers can forward packets from a subnet to another. They add the IP of their interface - which first received the dhcp request - in the request so that the dhcp server knows what IP to give. I've seen it, but I had not access to the dhcp server's config, so I don't know how this could work with Linux box (how to set up the Linux router ? How to set up the Linux dhcp server ?)

I wonder about these last 2 questions for a long time... I'll create another thread for these.