help :giaddr

abhijit khadatare anks030 at gmail.com
Thu Oct 16 11:53:16 UTC 2008


thanks for ur helpfull reply.
my network topology is as below

client----->layer2-[switch]----->[if0]router[if1]-------[isc]dhcp server

layer2 switch is manager switch----192.168.1.46/24
router interface0 -----192.168.1.1/24
router interface 1---192.168.2.5/24
dhcp server ------192.168.2.1/24

i'm putting giaddr as layer2 switch which is 192.168.1.46
 PROBLEM  is discover is reached upto the server ,but we dont get any offer
routing table is as below
#route -en
Kernel IP routing table
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0
eth1
192.168.0.0     0.0.0.0         255.255.255.0   U         0 0          0
eth0
0.0.0.0         192.168.0.1     0.0.0.0         UG        0 0          0
eth0

but when i add static route for 192.168.1.1 on server

#route -en
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt
Iface
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0
eth1
192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0
eth1
192.168.0.0     0.0.0.0         255.255.255.0   U         0 0          0
eth0
0.0.0.0         192.168.0.1     0.0.0.0         UG        0 0          0
eth0

then we got offer we saw on wireshark that
discover   from 192.168.2.5 to 192.168.2.1
offer from 192.168.2.1 to 192.168.1.46
port unreacheable..

hope that problem is much explore now...
thanks in advance
regards,
abhijit



On Tue, Oct 14, 2008 at 7:02 PM, Glenn Satchell
<Glenn.Satchell at uniq.com.au>wrote:

>
> >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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