How DHCP decide which scope to give thourgh dhcp relay agent?

Hi ,

I did some research and know that dhcp realay agent will modify the DHCP
request info and add some info on the giaddr field to indetify the source so
that DHCP will know which scope to give .

Anyone have more details docs related on this design ? Like what is the info
store in giaddr field ? how the dhcp server calculate and decide which scope
to give ?

If in multiple VLAN enviroment , my client pc is getting other VLAN IP .
What is the possible causes ?

DHCP is a very simple setup. The client broadcasts on the network with a
request. If there is a DHCP server which can receive the request, it replies
with an offer of an IP in the same subnet as the NIC in the server which
received the broadcast request.

If there is only a relay agent to receive the request, it will forward
the request to a DHCP server. The DHCP server will make an offer in the same
IP subnet as the NIC of the relay agent which recieved the original
broadcast.

"cs" <(E-Mail Removed)> wrote in message
news:420906F6-BEB3-423A-8965-(E-Mail Removed)...
> Hi ,
>
> I did some research and know that dhcp realay agent will modify the DHCP
> request info and add some info on the giaddr field to indetify the source
> so
> that DHCP will know which scope to give .
>
> Anyone have more details docs related on this design ? Like what is the
> info
> store in giaddr field ? how the dhcp server calculate and decide which
> scope
> to give ?
>
> If in multiple VLAN enviroment , my client pc is getting other VLAN IP .
> What is the possible causes ?

Thanks for reply .. ok now .. What you mean by same Ip subnet ? If my
enviroment is have multiple VLAN configure in the same switch and dhcp server
at other vlan network . So what will be the ip subnet on client if it on vlan
1 ?

vlan 1 10.10.1.x 255.255.255.0
vlan 2 10.10.2.x 255.255.255.0
vlan 3 10.10.3.x 255.255.255.0 (dhcp server ip range)

Because my understanding is client will first register as 0.0.0.0
255.255.255.255 . So how do dhcp know it should issue which scope ?



"Bill Grant" wrote:

> DHCP is a very simple setup. The client broadcasts on the network with a
> request. If there is a DHCP server which can receive the request, it replies
> with an offer of an IP in the same subnet as the NIC in the server which
> received the broadcast request.
>
> If there is only a relay agent to receive the request, it will forward
> the request to a DHCP server. The DHCP server will make an offer in the same
> IP subnet as the NIC of the relay agent which recieved the original
> broadcast.
>
> "cs" <(E-Mail Removed)> wrote in message
> news:420906F6-BEB3-423A-8965-(E-Mail Removed)...
> > Hi ,
> >
> > I did some research and know that dhcp realay agent will modify the DHCP
> > request info and add some info on the giaddr field to indetify the source
> > so
> > that DHCP will know which scope to give .
> >
> > Anyone have more details docs related on this design ? Like what is the
> > info
> > store in giaddr field ? how the dhcp server calculate and decide which
> > scope
> > to give ?
> >
> > If in multiple VLAN enviroment , my client pc is getting other VLAN IP .
> > What is the possible causes ?
>
>

It should not make any difference if you have VLANs. VLANs are just a
construct built into the switch. As far as the networking protocols are
concerned the network looks exactly the same, whether you have VLANs or
simple hub/switches and routers. If a machine is in the VLAN which is using
10.10.2.x and it broadcasts a DHCP request, that request will be received by
a DHCP relay agent on an interface with a 10.10.2.x IP address. The
broadcasts should not be crossing the "routers" between the subnets.

"cs" <(E-Mail Removed)> wrote in message
news:E6AEBF52-8DA0-47EC-BC63-(E-Mail Removed)...
> Thanks for reply .. ok now .. What you mean by same Ip subnet ? If my
> enviroment is have multiple VLAN configure in the same switch and dhcp
> server
> at other vlan network . So what will be the ip subnet on client if it on
> vlan
> 1 ?
>
> vlan 1 10.10.1.x 255.255.255.0
> vlan 2 10.10.2.x 255.255.255.0
> vlan 3 10.10.3.x 255.255.255.0 (dhcp server ip range)
>
> Because my understanding is client will first register as 0.0.0.0
> 255.255.255.255 . So how do dhcp know it should issue which scope ?
>
>
>
> "Bill Grant" wrote:
>
>> DHCP is a very simple setup. The client broadcasts on the network with
>> a
>> request. If there is a DHCP server which can receive the request, it
>> replies
>> with an offer of an IP in the same subnet as the NIC in the server which
>> received the broadcast request.
>>
>> If there is only a relay agent to receive the request, it will
>> forward
>> the request to a DHCP server. The DHCP server will make an offer in the
>> same
>> IP subnet as the NIC of the relay agent which recieved the original
>> broadcast.
>>
>> "cs" <(E-Mail Removed)> wrote in message
>> news:420906F6-BEB3-423A-8965-(E-Mail Removed)...
>> > Hi ,
>> >
>> > I did some research and know that dhcp realay agent will modify the
>> > DHCP
>> > request info and add some info on the giaddr field to indetify the
>> > source
>> > so
>> > that DHCP will know which scope to give .
>> >
>> > Anyone have more details docs related on this design ? Like what is the
>> > info
>> > store in giaddr field ? how the dhcp server calculate and decide which
>> > scope
>> > to give ?
>> >
>> > If in multiple VLAN enviroment , my client pc is getting other VLAN IP
>> > .
>> > What is the possible causes ?
>>
>>