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DHCP packet between hosts gets lost.

  1. The server sends DHCPOFFER to client.
  2. Client gets DHCPOFFER from server.
  3. Client sends back DHCPREQUEST.
  4. Server does not receive the DHCPREQUEST packet.

Can anyone suggest what could be the reason for this?

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Can you post part of your DHCP log showing this happening? – Joseph Nov 30 '09 at 5:50
Best to provide a complete tcpdump output, captured with -e. – womble Nov 30 '09 at 6:40

If you telling that server is not receiving DHCPREQUEST packet based on tcpdump or wireshark where no packets got dropped then it is network issue. Check ARP entries on client for servers IP address.

If you are telling server has not received packet using some other mechanism then check that server can receive UDP packets with source port 68 (basically check firewall is not blocking UDP packets). I would recommend using a casual rule like allow all UDP for small duration of testing if security is not a big concern.

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I know it sounds improbable, but perhaps the route from the client to the server might not support fragmentation, and the client is sending packets that are too big. This, supposing that

  • you are sniffing on the server
  • there are no firewalls or other things in between
  • client can send packets to server of smaller size

...and that you have verified all of the above.

And yes, that was an interview question I was asked once :)

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