DHCP option 82 behavior

Nicoson Dave Dave.Nicoson at thomson.net
Fri Sep 8 14:54:00 UTC 2006

-----Original Message-----
From: dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] On
Behalf Of Curt Rask
Sent: Thursday, September 07, 2006 1:59 PM
To: dhcp-users at isc.org
Subject: DHCP option 82 behavior

Hello all,

We have some equipment which is doing DHCP snooping, which means that it

forwards DHCP packets on through to upstream devices within their 
originating network.  Prior to sending the packets on, they insert 
option 82 information.  If the packets are received by the DHCP server 
on the same logical network, it fails to include the option 82 
information in the DHCP replies & acks.  Unfortunately, due to the 
implementation of DHCP on the network devices, this causes a breakdown 
in the process (the box tries to prevent flooding the dhcp replies out 
to all user ports for security purposes) as it no longer 'knows' which 
port the request came from.

In reading the RFC, it suggests that anytime a DHCP server receives 
option 82 information, it should always be contained in the reply or 
whatever communication is going back to the client.  Does anyone know of

a way to enable the inclusion of option 82 information for a local



It seems that the DHCP server receives traffic directly from the hosts
and not through a relay in the case of the local subnet.  So the packets
that reach the DHCP server don't contain an option 82, right?

And you want to force the server to send a faked option 82 anyway.  Is
that right?  

My initial reaction is to add an actual relay in between the clients and
the server, but I'm probably missing something about your problem.

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