On Thu, Jun 04, 2009 at 12:52:41PM -0700, Ted Lemon wrote:
> This raises an interesting question - in several places RFC3115 talks about
> a "valid Reply message," but the term is never defined. We aren't told
> what makes a Reply message "valid" or "invalid." So I understand the
> writer's confusion, and this ought to be clarified. I would assume that
> "valid" means "well-formed," which is to say "parses without encountering
> anything the RFC hasn't told you how to parse." You've been told how to
> parse options, so I would say that an unknown option is valid in this
> context, but the RFC provides no guidance.
There are message validation sections in 3315 that describe how to
validate the various kinds of messages (must contain this and that,
must not contain those other things...). I've always assumed that
valid, in the context of 3315's own lexicon, means that the message
has passed those tests.
I'm becoming increasingly aware of a different but related open issue
in both DHCPv4 and DHCPv6 - the client's selection criteria when
presented with multiple offers (or advertises).
DHCPv4 describes a selection period, but doesn't hint at selection
mechanisms. 3315 hints, which I've tried to implement to the best
of my ability, but is self-inconsistent in its hints, and
inconsistency in client implementations here could lead to
interoperability issues.
In particular, in either protocol, if a client de-selects a server's
offer due to some failing criteria ("i require options x,y,z to
operate, you did not supply z"), the server (and operator) has no
feedback to understand the nature of the deselection. The client is
simply silent in this case, which is identical behaviour to UDP packet
loss.
At some point I'll set forward to do something about that ("write a
draft"), but at least for me that time is not today. If someone else
has the energy, I think it would be good for there to be an optional
to implement selection algorithm, that also introduces a new option
for a client to advertise the results of selection, and a new message
so that option can be used when selection resulted in zero leases
(without declining the lease).
That's also an opportunity to reinforce simple ideas like, if you
see a new option you don't understand, ignore it.
--
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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