help :giaddr

Glenn Satchell Glenn.Satchell at uniq.com.au
Tue Oct 14 13:32:33 UTC 2008


>Date: Tue, 14 Oct 2008 18:51:35 +0530
>From: "abhijit khadatare" <anks030 at gmail.com>
>To: dhcp-users at isc.org
>Subject: Re: help :giaddr
>
>Thanks for reply.
>my network topology shown below
>
>
>client >|------------>layer 2 switch------------>dhcp server
>
>layer 2 switch ip 192.168.1.46/24
>dhcp server ip 192.168.1.2/24
>i recognised the problem
>problem is in dhcpd.conf
>i checked in conf file that
>
>if exists agent.circuit-id {
>option agent.circuit-id = option agent.circuit-id ;
>
>log(info , ("echo back circuit-id"));
>
>}
>
>if exists agent.remote-id {
>option agent.remote-id = option agent.remote-id ;
>}
>
>when giaddr =0 that contain opt82 frame then it is go working
>but when giaddr non zero (request from different subnet)
>server itself echo back opt82 frame no need to this checking.
>can u tell me what happen in following scenerio
>
>client------>layer2switch:1-------->layer2switch:2------>layer3switch:3----dhcp
>server
>
>each layer 2 switch act as relay agent then how giaddr flow,whether it
>should overwrite or not?
>thanks in advance.

Each of the switches is configured to forward the dhcp broadcast
requests to the dhcp server. dhcp-relays are not configured like a
router with the next hop, rather each is configured with the
destination dhcp server.


For the client in the example above layer2switch:1 acts as a relay
agent and uses unicast to forward the request to the dhcp server. The
other switches do not see the broadcast and are not involved in the
relaying of this client's request. The unicast packet will have
layer2switch:1's address in the giaddr field.

regards,
-glenn



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