DNS vs. DHCP

jscimeca715

I apologize if everyone thinks this is in the wrong forum, but I had a question that came up last night that my mind was telling me I was right but I couldn't get over the possibility that I could be wrong.

A DNS server could be on a different subnet when configured on a host but a DHCP server has to be on the same subnet.

The above statement is correct right? The reasoning would be the host broadcasts to a DHCP server and receives the DNS information (possibly) from that reply.

Any help would be appreciated.

meadIT

Both DNS and DHCP could be on any subnet. If you do not have a DHCP server on your subnet, you do need a DHCP relay agent though (can be a RFC 1542 compliant router or another computer acting as the agent). The Relay Agent just acts as a middle man. It picks up the DHCP Discover broadcast packet and forwards it to the DHCP server.

APA

technically no... the DHCP server can be in a different subnet...

It's a matter of turning the DHCP broadcast into a unicast request...

On Cisco devices you can utilize the 'ip helper-address x.x.x.x' command on a gateway interface to tell the router to forward all DHCP broadcasts as unicast requests to the host specified.

Traditionally you would put a DHCP server in the local lan to negate the need to use 'ip helper-address'.... but to answer your question... it is possible to have a DHCP server in a different subnet.

jscimeca715

That's why this site is the bomb. Thanks guys.