# DHCP relay not working



## seth_turner_04 (Sep 20, 2006)

I'm trying to get DHCP relay working on my 3Com 5500 switch, but not having any luck. Maybe there are some guys on here who run 3Com equipment that can help me out.

I have two subnets, a 10.30.x.x and a 20.1.1.x. A test machine is hooked up on the 20.1.1.x subnet and the dafault gateway of the interface is 10.20.0.1. My DHCP server is on the 10.30.x.x subnet and has the ip 10.30.0.24.

I setup the DHCP server with a 20.1.1.2 - 20.1.1.254 address range.

On the 3com 5500 switch, I entered the following commands.

[5500G-EI] dhcp enable
[5500G-EI] dhcp server 1 ip 10.30.0.24
[5500G-EI] udp-helper enable
[5500G-EI] interface vlan-interface 20
[5500G-EI-Vlan-Interface20] udp-helper server 10.30.0.24
[5500G-EI-Vlan-Interface20] dhcp server 1
[5500G-EI-Vlan-Interface20] ip address 20.1.1.1. 255.255.255.0

Whenever I do an ipconfig /release and /renew, I still do not receive an IP address from the DHCP server.


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## Cellus (Aug 31, 2006)

Where is the switch located in the topology? If there is something like a router which is between the subnets and switch, the router may need to be configured to relay (ie. be a DHCP agent).


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## seth_turner_04 (Sep 20, 2006)

Oops I seen I made a typo. The 20.1.1.x subnet has a default gateway of 20.1.1.1. I don't know why I put 10.20.0.1.

Anyways, each subnet interface is on a 3com 5500 switch. Each is a separate VLAN. The commands that I typed were done on the 3com 5500 switch. It is a layer 3 capable switch also.

Here's a pic of the topology.


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## seth_turner_04 (Sep 20, 2006)

I did a packet trace on the server and the workstation at the same time. This is what it shows.

The DHCP server just shows normal traffic from the same physical subnet.
Source Destination Info
10.30.0.24 10.30.2.168 DHCP_ACK
10.30.0.24 10.30.0.103 DHCP_ACK
10.30.0.24 10.30.2.25 DHCP_ACK

This is what the workstation shows.
Source Destination Info
0.0.0.0 255.255.255.255 DHCP_DISCOVER
0.0.0.0 255.255.255.255 DHCP_DISCOVER
169.254.213.231 255.255.255.255 DHCP_INFORM
169.254.213.231 255.255.255.255 DHCP_INFORM

Does this mean that the switch is the problem still? It looks like a very simple setup so I don't see how it could be wrong.


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