dhcrelay problems

[Glenn Satchell]

>From: Chris Cohen <kildau-ml at gmx.de>
>To: dhcp-users at isc.org
>Subject: dhcrelay problems
>Date: Sat, 25 Aug 2007 17:39:08 +0200
>
>Hi,
>
>I've got the following setup:
>
>router1
>vlan10: 10.1.0.1/24
>vlan11: 10.1.1.1/24 (dhcp works fine via wired network, but without dhcrelay)
>[...]
>vlan13: 10.1.16.1/30
>
>router2:
>eth0.1: 10.1.16.2/30
>br0 (eth1 + eth0.0): 10.1.16.129/25
>
>I started dhcrelay at router2 using:
>dhcrelay -i br0 -a 10.1.16.1
>
>A dhcpd is running at router1 with the following configuration:
>shared-network TESTNET {
>        option  domain-name "example.org";
>        option  domain-name-servers 10.1.3.2;
>        subnet 10.1.1.0 netmask 255.255.255.0 {
>                option routers 10.1.1.1;
>                range 10.1.1.129 10.1.1.254;
>        }
>}
>
>shared-network WLAN {
>        option  domain-name "wlan.example.org";
>        option  domain-name-servers 10.1.3.2;
>        subnet  10.1.16.0 netmask 255.255.255.0 {
>                option routers 10.1.16.129;
>                range 10.1.16.130 10.1.16.154;
>        }
>}
>
>My Laptop (running Ubuntu) doesn't get a DHCPOFFER. The only thing I can see 
>is
>forwarded BOOTREQUEST for 00:11:e0:02:24:2d to 10.1.16.1
>forwarded BOOTREQUEST for 00:11:e0:02:24:2d to 10.1.16.1
>forwarded BOOTREQUEST for 00:11:e0:02:24:2d to 10.1.16.1
>forwarded BOOTREQUEST for 00:11:e0:02:24:2d to 10.1.16.1
>on router2 when I start dhcrelay with -d. Nothing in the logs on router1.
>
>Is there anything wrong with my setup?
>
>-- 
>Thanks
>Chris

dhcrelay needs to be told to listen on the interface that it will
receive replies back from the dhcp server. So for your network it needs
to listen on eth0.1 as well as br0. If this is now all the interfaces
on router2 then you can run it without the -i parameters, otherwise you'll
need -i br0 -i eth0.1

This is from the dhcrelay man page:

     The -i flag can be used to specify the network interfaces on
     which  the  relay agent should listen.   In general, it must
     listen not only on those network interfaces to which clients
     are  attached, but also on those network interfaces to which
     the server (or  the  router  that  reaches  the  server)  is
     attached.

regards,
-glenn