Two network cards, different VLANS and DHCP requests

Question

Our network is is setup with two different VLANS, VLAN1 and VLAN2, VLAN1 is our computer system and VLAN2 our telephone system. There is no routing between the VLANS, VLAN1 has 2003 as a DHCP server and VLAN2 uses the phone system to give out IP Addresses.

We have some computers that need access to both VLANS, and we've achieved this by using two NICS and statically assigning IP addresses. We've now come to apoint where there are enough computers that we don't want to manually manage IP addreses on VLAN2.

The issue is that when set to DHCP NIC2 on VLAN2 is being assigned an IP address from the DHCP server on VLAN1. If we unplug the network card on VLAN1, then the correct IP address is being assigned, there is no routing as it's not possible to access the IP address on NIC2/VLAN2 from anywhere on VLAN1 once it has been given.

I'm curious as to why this is happening, I've been unable to find anything specific but my general feeling is that XP broadcasts DHCP requests over both network cards, even if it is only one card that is requestsing it, the 2003 DHCP server is responding on Card 1 with a higher priority, so card two is using that responce.

Answer 1

this sounds like a bad idea to set it up in this way. I would have given the 2003 server 2 NICS and enabled the routing and remote access on it. Clients in vlan1 could then route to vlan2 via the server where we could implement some basic filtering and firewall rules.

You Could then configured the server as a dhcp server for both vlans by adding the appropriate scopes and setting the DHCP relay agent in the routing and remote access config. this way only the server requires 2 NICS

Answer 2

I suspect that the PC's have the two networks 'bridged' so they are broadcasting the DHCP requests. I'd check the 'Network Connections' screen on the PC's.

However, I agree with MikeT, there are other ways to skin this. You could use a server with two NICs, or if you really have VLANs (not just two subnets), then your networking equipment likely has a facility for setting routes between VLANs, and setting security on who/what can acccess those routes.