DHCP relay & IPoIP tunnel

Vincent CATROS vincent.catros at laposte.net
Mon May 23 08:33:36 UTC 2011


I have a problem with my DHCP relay and it seems to be related to IPoIP tunnels.

The relay has 3 ethernet interfaces.
- eth0 is connected to LAN-1 (subnet
- eth1 is connected to LAN-2 (subnet
- eth2 is connected to the upstream network (subnet

On eth2 I have an IPoIP tunnel and, hence, a "tunl1" virtual interface.
"tunl1" @IP is
the other end of the tunnel is

The routing configuration of my network and my relay is such that the downstream and upstream trafic from/to LAN-2 pass through the tunnel.

My relay is on a Linux Debian Squeeze
version of ISC relay is 4.1.1-P1

The command line I run is :
dhcrelay -d -i eth0 -i eth1 -i eth3

For LAN-1 every thing works properly.

The problem is that DHCPOFFER to LAN-2 (through) the tunnel are not forwarded to the client.
dst.addr of the packet is good ( The packet seems well formed (yourip is chaddr is good)

Any idea?


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