DHCP Relay agent not forwarding messages to the client

Gero Palacio gero.palacio at gmail.com
Mon Jun 15 20:52:53 UTC 2015


Hello.

I'm currently setting up a test network with a DHCP relay agent that it's
not communicating back to the client with the corresponding DHCP server
offers. So the client keeps sending discovery messages, the relay agent
forwards those messages to the servers, receives the responses and does not
pass them along to the client.

*Setup:*

CLIENT <---> [eth0] (relay agent) ROUTER-1  [eth1] <---> ROUTER-2 <--->
DHCP Server

The relay agent *runs ONLY on the interface that faces the client*, which
is eth0: "dhcrelay -4 -i eth0 10.0.1.10"

tpcpdump and Wireshark both show that the discovery message from the client
are being forwarded to the server. The server replies with an offer, with
the correct dst ip address (interface of R1 facing the client, eth0 on R1),
reaches interface eth1 on R1 and but does not gets to the client. The
transaction ID mataches on all messages and the option "Relay agent IP
address" is set with the correct ip (eth0 on R1).

Can anybody tell me if I'm doing something wrong? Is this a known bug?

ISC DHCP version 4.2.8.

Thanks all,
Gerónimo.
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