Host options and DCHP-Inform (Was: [RESOLVED !!!] Multi Homed DHCP - VLANs, Hosting Remote Subnets - Working With DHCP Relay Agent)

Simon Hobson dhcp1 at
Tue Mar 19 18:52:59 UTC 2013

"Friesen, Don CITZ:EX" wrote:
> I have scanned all the release fixes as they came out, without seeing the following fixed.  And since the servers have been working flawlessly the way they are configured... other pressures drive my time.
> We have hundreds of shared networks with multiple subnets inside each.  I had originally optimized the options by placing the common default options at the highest level I could.  However, we had many cases where we needed to give different options to certain workstations.  We defined those options in the 'group' statement for those workstations.  It would work... for a little while.  At the first INFORM packet, the ACK that went back contained NOT the options from the group statement, but the global options from the subnet statement, breaking the required service.  I have since recoded and my script that builds the configuration files from the Oracle database now place all options at the lowest level, inside the pools... so that the hardware reservations will retain the options they need.

That is a known issue - and it's not likely to be fixed since I believe it's required by the RFCs.
Someone else will have to fill in the details, but I believe that in response to a DCHP Inform message, the server is not allowed to consider any leases the client may hold - only to look at the config and send out the options appropriate to the subnet. Whether it's valid to argue that a host statement with matching selection criteria should be part of the scope when determining options is another matter.

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