DHCP option 82 behavior

Curt Rask crask at telesyn.com
Thu Sep 7 17:59:07 UTC 2006

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 subnet?



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