DHCPINFORM

[Randall C Grimshaw]

Exercise caution here. In cases where multiple switches reside at layer2, including aggregators, configured to inject option-82 "AS A RELAY" - they will ALL see the broadcast and you will receive multiples. ... Think of the seagulls in 'Finding Nemo' all crying 'mine, mine, mine, mine, mine, mine, mine, ...'.


From: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Marty Sørensen
Sent: Wednesday, February 04, 2009 11:22 AM
To: Glenn Satchell; Users of ISC DHCP
Subject: Re: DHCPINFORM

Hey Glenn,

What if you have some L2 device (where the client is connected), not the L3 relay, that does DHCP snooping and add's option-82 in the packege for validating the DHCP request, this is then dropped by the switch because the server strip's the option-82 :-(

Martin
On Wed, Feb 4, 2009 at 2:02 PM, Glenn Satchell <Glenn.Satchell at uniq.com.au<mailto:Glenn.Satchell at uniq.com.au>> wrote:

>Date: Wed, 4 Feb 2009 13:44:36 +0100
>Subject: Re: DHCPINFORM
>From: Marty Sørensen <buzzwork at gmail.com<mailto:buzzwork at gmail.com>>
>To: Users of ISC DHCP <dhcp-users at lists.isc.org<mailto:dhcp-users at lists.isc.org>>
>X-BeenThere: dhcp-users at lists.isc.org<mailto:dhcp-users at lists.isc.org>
>
> Hey Randall,
>
> Thanks for the reply. It seens that the switch relay's the option-82 OK, in
> this case, but the server drops it ?
>
> Martin
>
DHCPINFORM is unicast to the dhcp server, so the switch's relay never
sees it. Relays only see broadcast packets, then add the option-82 and
forward tot he dhcp server.

See the posts earlier today about how responses to DHCPINFORM don't
look at existing lease data. This includes any options added by the
relay when it processed the DHCPDISCOVER.

regards,
-glenn

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