Bug? INFORM and REQUEST getting ACK'ed with different DNS server lists (3.0.4, 3.1.1, 3.1.2)

Jeffrey Hutzelman jhutz at cmu.edu
Wed Feb 4 17:33:16 UTC 2009

--On Tuesday, February 03, 2009 10:23:48 AM -0800 "David W. Hankins" 
<David_Hankins at isc.org> wrote:

> On Tue, Feb 03, 2009 at 06:35:58PM +0100, Axel Beckert wrote:
>> As far as I understand DHCP there should be no difference in any of
>> the server lists equal if the query was a DHCP REQUEST or a DHCP
>> INFORM packet.
> There is a strange MUST in RFC 2131 that says a DHCP server "MUST
> NOT check for an existing lease" when processing a DHCPINFORM.  My
> interpretation is that we can't source the client's dynamic lease, and
> therefore can't pull any information from lease binding scopes or the
> pool it belongs to.  We can't source fixed-address host records
> ("static leases" are still leases).

Hrm.  I wonder if the intent there is not the behavior we currently have, 
but rather to require that DHCP servers handle DHCPINFORM even when the 
client doesn't have a lease; for example, when it has manual address 
configuration but wishes to get other parameters from DHCP.

I also think the current behavior of treating a host record with a 
fixed-address differently from one without is not the best approach.  Sure, 
the fixed-address indicates the existance of a static lease, but it 
shouldn't also imply that the options and statements in the host 
declaration cannot be used other than as part of that lease.

As a result of this behavior, we end up having to emit two nearly-identical 
host declarations for every host, simply because the server won't use a 
host declaration with a fixed-address when constructing a dynamic lease.

-- Jeff

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