DHCP Snooping - Option 82...I'm confused

opers13 · ‎07-29-2009

So, I'm under the impression that after I enable Option 82 on the switch, I would see the client switchport info show up on my Windows 2008 DHCP server..is that right??

Peter Paluch · ‎07-29-2009

Hello,

After you activated adding the option 82 to the DHCP packets on the switch, it should be visible in DHCP packets forwarded to your server. However, it is up to your Windows 2008 DHCP server what will it do with that information - whether it displays it somewhere or whether it uses it in its IP address assignment logic. I am sorry that I can't tell you anything more as I am not familiar with Windows DHCP servers.

Best regards,

Peter

opers13 · ‎07-30-2009

Thanks Peter. From the little bit of info out there, the DHCP server(in this case 2008 server) has to accept/read option 82 from DHCP packet.

My clients are getting DHCP from the server...therefore I'm assuming 2008 server is accepting/reading Option 82 from DHCP packet...but now what? where to do find the Option 82 info on my 2008 server??

Peter Paluch · ‎07-30-2009

Hello,

Try to at least confirm that the Option-82 is present in the DHCP packets coming to your DHCP server. The Wireshark packet sniffer should do a great job here.

Besides that, I somehow doubt that your Windows 2008 server will show you the Option 82 in a readable form. Its format is vendor-dependent and may vary wildly. Perhaps it can be found somewhere in your DHCP server's lease database. The Option 82 is primarily here to aid the Relay Agents forward the DHCP responses properly to clients (without broadcasting them to every member of a network) and perhaps to facilitate some advanced assignment policies on the DHCP server. The possibility to use this option as a monitor tool to see where your individual clients are connected is surely tempting but I think that is only a side effect and the option 82 was never designed with this use primarily in mind.

Best regards,

Peter