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

Friesen, Don CITZ:EX Don.Friesen at
Tue Mar 19 19:41:22 UTC 2013

   Last few times I read the RFC I didn't see it in the right light.  The RFC statement:

   "If a client has obtained a network address through some other means (e.g., manual configuration), it may use a DHCPINFORM request message to obtain other local configuration parameters."

   Is key.  A machine that has obtained a lease via DHCP should not be using a DHCPINFORM message.  Hence the fault is not in the DHCP server, it is doing exactly what it should.  The fault is with the Microsoft implementation of the DHCP client.  It is erroneously issuing DHCPINFORM messages which are only valid if the address was NOT obtained via a call to DHCP.

Don Friesen

-----Original Message-----

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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