Troubleshooting Guide

Troubleshooting DHCP Relay
Before you begin
• Configure the server to reply to the client subnet. Check the server configuration file to verify
the configuration.
• Configure a route on the server for the client subnet to create a path on which to send replies.
About this task
Perform this procedure to troubleshoot the DHCP relay agent.
Procedure
1. Verify that the interfaces that link the client and server are up, and that the ports are in the
forwarding state.
a. To verify client availability, you can configure a temporary static IP address on the
client, and then use the ping command.
ping WORD<0-256>
b. To verify the port is in the forwarding state, use the following command for the slot and
port number:
show spanning-tree [rstp|mstp] port role [{slot/port[-slot/port]
[,...]}]
If STP detects loops in the configuration, it blocks ports to avoid flooding in the network.
In this situation, the port is not in the forwarding state.
2. Ensure that DHCP is enabled on the client interface and that a valid forwarding path exists
and is enabled. Ensure the server is reachable.
3. View the statistics counters for the relay.
4. If request or reply counters do not increase, use a sniffer tool to ensure that the client sends
the packets, and that the interface module receives the packets.
You can configure mirroring for the ingress port to verify if the packets reach the module.
a. If the client sends the packets, check that the packets reach the CPP and search the
trace results for the ingress port:
trace level 9 3
trace grep WORD<0-128>
b. If the packets reach the CPP, check that they reach the DHCP protocol; check for errors
or packet drop messages:
trace level 170 3
trace grep WORD<0-128>
5. If Option 82 is enabled, check the statistic counters for dropped packets, and perform a trace
for the DHCP protocol:
Upper layer troubleshooting
January 2017 Troubleshooting 226
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