Duplicate lease, different ip.

David W. Hankins David_Hankins at isc.org
Wed May 2 21:28:14 UTC 2007

On Mon, Apr 30, 2007 at 12:11:18PM -0300, Bruce Hudson wrote:
>     However, the first time the server see a request with an identifier it
> will "upgrade" an existing lease for that client address that does not have
> one by adding it. The process is not reversible so any requests there-after
> without an idetifier are a different client. There was an ancient message
> to the list from Ted Lemon that called this "tragically unavoidable". 

This is only true IFF you are running an older version of the software
(with a bug) and the client that has a uid and identical chaddr has
"requested" the old address.  New versions will never 'upgrade' a
lease from chaddr-identified to client-identified.

That does not help someone who is using PXE because ping-before-offer
will successfully ping the PXE client, and abandon its lease, so even
the old software won't work.

I'm not sure it's unavoidable.  But it's "working as intended" that
these two clients get different leases.  This was Ted's interpretation
of RFC2131, and I share it.

It's certainly tragic.

I wanted to get a feature into 3.1.0 that would help administrators
sort client identification problems out using config syntax (with an
eye towards the future which is RFC4361).  We cut 3.1.0 to alpha
before I could start on that feature.

I don't remember if didi wrote a second patch, but the one I
remember disabled the client-identifier entirely...this is not
something we feel we can incorporate in the official software.

David W. Hankins	"If you don't do it right the first time,
Software Engineer		you'll just have to do it again."
Internet Systems Consortium, Inc.	-- Jack T. Hankins

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