multiple dhcp relay configuration

[Glenn Satchell]

>Subject: multiple dhcp relay configuration
>Date: Tue, 7 Nov 2006 14:52:15 +0530
>From: <tajinder.pal at wipro.com>
>To: <dhcp-users at isc.org>
>
>Hi,
>
>I am trying to configure two relays both at different nets and one
>client and one server connecting like below
>
>
>DHCP Client  ------------------------->  DHCP Relay 1
>-------------------->   DHCP Relay 2   ----------------------->  DHCP
>Server
>            eth0       192.168.2.x     eth0         eth2    192.168.1.x
>eth2         eth1      192.168.0.x      eth1 
>
>How should I give configuration so that Client can have IP address.  I
>am using open source dhcp-3.0.3 from ISC with Linux kernel 2.6
>
>I have following configuration which is not working   ( It is working in
>case I remove one Relay)  ?
>
>Relay 1 -->
>
>dhcrelay -i eth0 -m forward 192.168.0.1(which is server)
>
>Relay -->
>
>dhcrelay -i eth2 -m append 192.168.0.1
>
>It is not working, please suggest solution.

dhcrelay needs to listen on the other interface for replies from the
dhcp server, so if you remove -i eth0 and also -m forward and -m append
you should ok.

Usually you only need something such as this on your relay hosts:

  dhcrelay 192.168.0.1

man dhcrelay
...
     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.    However,  in  some cases it may be necessary to
     exclude some networks; in this case, you must list all those
     network  interfaces that should not be excluded using the -i
     flag.

As mentioned by Simon in an earlier reply, dhcrelay listens for
broadcasts then forwards them as a regular unicast packet to the dhcp
server using normal IP routing. So dhcrelay is not required on DHCP
relay 2 for packets from relay1 to get to the dhcp server.

regards,
-glenn
--
Glenn Satchell     mailto:glenn.satchell at uniq.com.au | Some days we are
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