Hi there

I recently replaced a switch in my IT network. I have a vlan set up for access ports and then another for voice.

The IT switch was connecting with fibre to a stack switch and was sharing the stack L3 switch uplink to the core switch. The initial vlan resided in this switch as well.

So I decided to upgrade the network a bit. I replaced the IT switch with a 3750 and connected the fibre directly in the core and moved the vlan to the IT switch. All worked fine if you had a static ip. Configured the uplink with and IP or a trunk port, tried both.

The problem is that the DHCP server that was sitting in a different ip range couldn't send the DHCP reply's any more. It would receive it from the network, but as soon as it tries to send the ack back to the network, it said on wireshark that the network is not reachable, but i could ping it from the same server.

I did enable ip helder on the vlan. I tried different settings on the uplink port, even moving the vlan to the core switch nothing seems to work for the dhcp request to be sent to the IT switch. I have no access list enabled.

Any suggestions will do?

Thanks

I have a Windows 2003 DHCP server, and the "connection" port was setup as a trunk then I decided to make /30 IP address to connect the two switches, both methods gave the same results.

NM_IT01#sh run int gi 1/0/49 Building configuration...

Current configuration : 123 bytes ! interface GigabitEthernet1/0/49 description NM-BLDG3-S-SWC01 no switchport ip address 10.20.37.2 255.255.255.252 end

This is the config for the IT switch.

Cisco,

Have you checked to see if the DHCP server actually has a route to the IT Data and Voice subnets?

You said that the DHCP server was receiving the DHCP requests (which indicates that your DHCP relay is configured correctly), however the DHCP server is unable to send the DHCP offer back to those clients.

If the routes all look OK from the DHCP server's gateway (which I'm assuming is the core switch), I'd suggest you check the local route table on the DHCP server to make sure that it doesn't have some incorrect static routes for your IT Data and Voice subnets.