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dhcp

DHCP: stuck between DHCP offer and DHCP request

Here is an image of my current topology (this is a real topology, just added the packet tracer image so you can picture it):

topology
(source: smartplace.mx)

When when the client on the right sends the DHCP DISCOVER (broadcast), the router redirects it to the DHCP server with the IP of the gateway as source and IP of the DHCP server as destination (unicast).

The DHCP server then replies DHCP OFFER with its IP address as source and the fa0/1 IP address as destination (unicast).

However, this does not reach the client, and it does not reply with the following DHCP REQUEST.

Routing is fully configured in the router. Whenever I add another computer under the same subnet as the server, DHCP is successfully gone through.

Also, if i assign a static IP to this new host, I can ping and telnet the router and switch on the other network segment.

The only DHCP related configuration I have is the ip helper-address on both the switch and router gateway in the right side. The DHCP Server has the pool for both networks, and has the gateways also configured for both networks.

I cannot seem to find where and the reason this packet gets lost!

Solution

  • As it turns out, all we had to do was configure the relay agent in the gateway of the other networks. The problem we had was that the routers we were configuring were kind of old and did not support the DCHP proxy configuration for DHCP servers that were not the router's DHCP server. When we switched routers, we discovered everything worked just fine.

    A lot of great information for Cisco routers DHCP relay agent configuration can be found here:

    http://www.cisco.com/en/US/docs/ios-xml/ios/ipaddr_dhcp/configuration/15-sy/dhcp-relay-agent.html