Two offers in response to one discovery

John Miller miller at
Wed Dec 14 17:26:09 UTC 2011

Simon, I will try to get these posted, but the funny thing is that the log
only shows the offer we want (the noncompliant IP. It does not show the
offer for the compliant IP.

Will try to get these posted soon - John
-----Original Message-----
From: at
[ at] On Behalf Of
Simon Hobson
Sent: Wednesday, December 14, 2011 12:10 PM
To: Users of ISC DHCP
Subject: RE: Two offers in response to one discovery

John Miller wrote:

>A little more as to how Campus Manager works that might shed some light.
>Basically there are two pools; compliant and noncompliant. The MAC 
>address of a client moves from one pool to the other depending on their 
>state of, well, compliance with network policy. The move is done by 
>either having or not having the client MAC address in the table of 
>valid (compliant) MAC addresses. The situation with the client in 
>question is that it was compliant, then became noncompliant, so yes, at 
>one time it did have one of the IP addresses that is being offered. 
>When the DISCOVER is sent, the packet does contain a request for its 
>old IP address (option 50), but my understanding is that the server 
>should ignore this since the client MAC is not in the compliant table 
>(maybe a bad assumption). The server responds with the 2 offers; one 
>for the requested IP and the other (correctly) with a non-compliant IP. 
>The client only responds to the offer for wrong IP, which the server 
>properly NAKS. This goes on for some time until the server finally 
>sends an ACK for the compliant IP (like it gives up trying to do the 
>right thing) and then my non-compliant client is sitting on the compliant

Probably time to be posting server logs and config files - obviously only
relevant lines from the logs, and you'll need to thin out the config file.

Simon Hobson

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