Re: I never thought of this scenario

Grant Taylor <gtaylor@tnetconsulting.net> wrote:

Nope.  DHCP *IS* routable.  When you use DHCP relay agents, they use the
DHCP protocol to talk to the DHCP server.  They do so from known /
configured IP addresses and they are PERFECTLY HAPPY to send DHCP
requests through a routed IP network.

Although a DHCP relay agent is something like an application level
gateway. It is true that the communication between the relay agent and
the actual server MAY be Unicast, and is thus routable; the
communication between DHCP client and relay agent relies on broadcast
being available.

In fact, I believe that a DHCP client that used a DHCP relay helper to
obtain it's release originally is perfectly capable of communicating
with a remote DHCP server itself w/o the use of the helper.

DHCPDISCOVER is broadcast and needs a relay agent if the server is not
in the same broadcast domain. I am not sure wether the DHCPREQUEST
that a client uses to renew its lease (even when it's just rebooting)
is broadcast or not, I would not be surprised if it was.

I agree that DHCP is almost never routed.  But lack of doing something
doesn't mean that it's not possible to do it.

I think that in realistic deployments, the communiation between relay
agent and server is probably almost always routed.

Greetings
Marc
--
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Marc Haber         |   " Questions are the         | Mailadresse im Header
Rhein-Neckar, DE   |     Beginning of Wisdom "     |
Nordisch by Nature | Lt. Worf, TNG "Rightful Heir" | Fon: *49 6224 1600402