Re: dhcp / giaddr / configuration for giaddr update

On 24 Sep, 11:16, Merv <merv.hr...@xxxxxxxxxx> wrote:
if a dhcp server is connected to a router that connects many different
subnets... how does the dhcp server know which subnet a dhcp request
came from? does this information come from the giaddr field of the
dhcp request packet? if yes,
is the value of this field set to the
address of the of the router interface that originally received the
packet or the router interface that the packet is forwarded through?

yes this function is known as DHCP relay agent -

and does the giaddr update itself require any configuration of the
router device or does the router know to update it automatically? if
it requires configuration, how is it done? thanks for reading

on Cisco router yes - configured on the required interfaces wi the
command ip helper-address

"what happens in the case of a dhcp request being
forwarded through several routers before reaching the dhcp server"

The key thing is that the relay agent sends a unicast
to the dhcp server and not a broadcast so it travels
through the network unaltered to the dhcp server.
(clearly ttl field is decremented, etc.). Intermediate
relay agents don't see the packet at all.


.

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