Our topology is such that we have two 4510's in our IDF closets. Each switch has a data VLAN and a voice VLAN. The switches are layer 2 trunked to the core, where the VLAN interfaces are, routing happens, and DHCP is forwarded to the DHCP server.
What is the best practice to provide DHCP service redundancy? If there are two dhcp servers, and two "ip-helper" addresses, will the network only forward dhcp requests to the first IP as long as it's reachable from a network perspective? If it goes down, then dhcp goes to the second address?
What if the first server's dhcp service is having a problem – but the server is still reachable via the network (you can ping it, but dhcp service is down)? Or what if the DHCP scope is full? Will the second ip-helper address help? Will the second address only come into play if the first server is hard down?
Is there any way to get the ip-helper to "round-robin" between the two?
PS. Unfortunately, this is a Microsoft only DHCP Server option. I was asked about ideas and I mentioned Infoblox, but that's in the future …. maybe.
Thanks.
Best Answer
The router will forward all DHCP requests to all servers configured with ip helper. The first server to respond with a usable address wins. I'm unaware of a way to round-robin from the router.