dhcp relay

[Glenn Satchell]

>From: JOBY THAMPAN <JOBYTHAMPAN at nestec.net>
>To: "'dhcp-users at isc.org'" <dhcp-users at isc.org>
>Subject: dhcp relay
>Date: Tue, 25 Apr 2006 14:25:09 +0530
>
>Hi all,
>	I have a setup like this
>
>	 <<...OLE_Obj...>> 
>
>	First Linux Machine
>	Dhcp Server is started on eth0 interface and Eth0 ip is 192.168.20.1
>
>	Second Linux Machine
>	Eth0 got ip from dhcp server as 192.168.20.111
>	On Eth1 i started Dhcp Relay with ip 192.168.40.1
>
>	STA is a windows machine
>	I want to get an ip in the range 192.168.40.X
>
>
>	When STA renews the IP.  DHCP Offer is reaching upto Eth0 i/f of
>linux Machine 2 but not to the STA
>	and the dhcp offer is having its siaddr field 0.0.0.0
>
>	If anyone knows please help.
>
>Rgds
>Joby

Hi Joby

On the second linux machine you need to start the dhcp relay so that it
listens on the interfaces where requests will come in (eth1) and the
interface where the dhcp server is (eth0) so that it can hear the
responses from the dhcp server.

The man page for dhcrelay says:

     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.

In general starting dhcrelay with no interfaces specified will do the
right thing. The only parameter to use is the fqdn or ip address of the
dhcp server. In your case, something like this will probably be right:

     dhcrelay 192.168.20.1

regards,
-glenn