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

Simon Hobson dhcp1 at
Wed Mar 20 14:08:13 UTC 2013

"Friesen, Don CITZ:EX" wrote:
>   "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.

Leaving aside the inference that a device which got an address by DHCP shgouldn't then use DHCP Inform, I do think that Microsoft's approach is architecturally the right thing to do.
If you consider the DHCP client as a service, then other parts of the OS or userland software can use it to get config. The DHCP client itself should handle/know about as little as possible. So while the network code asks the DCHP client to get an address etc which is part of the basic setup - getting config for other software shouldn't (IMO) really be considered part of that. So when the user starts a web browser, it would seem reasonable to me for the browser to ask the DCHP service to see if it can get certain options for it - at which point the DHCP Inform is sent.

More information about the dhcp-users mailing list