Troubleshooting DHCP

About this task

Perform this procedure to troubleshoot the following Dynamic Host Configuration Protocol (DHCP) scenarios:

  • The client cannot obtain a DHCP address when in the same subnet.

  • The client cannot obtain a DHCP address when in a different subnet.

When the DHCP server and client are on the different subnets or VLANs, you must configure the device as a DHCP relay agent. The device must forward DHCP requests to the DHCP server. You must perform extra troubleshooting steps to troubleshoot the DHCP relay agent.

Procedure

  1. Check the physical connectivity between the DHCP client and server.
  2. Verify network connectivity by configuring a static IP address on a client workstation.

    If the workstation still cannot reach the network, the problem is not DHCP. Start troubleshooting network connectivity.

  3. Attempt to obtain an IP address from the DHCP server by manually forcing the client to send a DHCP request.

    If the client obtains an IP address after the PC startup is complete, the issue is not the DHCP server.

  4. Obtain an IP address on the same subnet or VLAN as the DHCP server.

    If the issue persists, the problem may be with the DHCP server. If DHCP is working on the same subnet or VLAN as the DHCP server, the DHCP issue can be with the DHCP relay agent.

  5. Confirm the DHCP relay agent configuration is correct.
  6. Obtain sniffer traces where the traffic ingresses and egresses the switch and also on the client side of the network.
  7. Check the logs on the switch for errors such as size exceeded or incorrect packet format.
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