single dhcp server with multiple subnets

[Simon Hobson]

"Senko, Mike" <Mike.Senko at seattle.gov> wrote:

> If I can obtain a cisco switch, I will. I think they do vlans very well...LOL


Yes they do, and it's something I've had to get my head around lately. Make sure you get a "real" Cisco switch, not a "Linksys with a Cisco badge" one with a "similar but annoyingly completely different" CLI. If it's just something for testing, you can get older units off eBay for next to nothing.

> The 10.1.6.2 address was on the router connected to the trunk
> port. I want to remove the router and just use the switch and its Relay Agent Config.

Not sure if that's just "poor phrasing" or if you are confused about the functions of the different elements.

A DHCP relay agent doesn't do any routing. It simply receives packets on one interface, adds teh GI-Addr field, and then puts the modified packet into the agents IP stack to be delivered to the server. There needs to be a route to the server - but that does not necessarily mean that the relay agent is doing the routing.

The router is responsible for taking packets from one interface and forwarding them to the appropriate interface to get closer to their destination.

Some switches include routing functions - then it gets confusing as you have to keep track in your mind whether you are configuring switching (Layer 2) or routing (layer 3) functions.

The TL;DR version :
You *need* a router somewhere in the network otherwise packets cannot be routed between subnets, and the relay agent will not be able to function.

I suspect from the config that your switch includes routing functions, given that it has IPs configured on multiple VLAN interfaces. Typically, on an L2 only device, you only configure an IP on the management VLAN/interface.