Subject: [dhcwg] RFC4361 adoption stumbling block.

From: "David W. Hankins" <[email-masked]>
Date: Tue, 26 Sep 2006 15:42:20 -0700

Below, I describe something that is unquestionably a bug - a bad
security glitch - and any such software should be discovered and rooted
out.  I do not mean to present this as a problem for the protocol, but
rather an operational issue (and there is no dhc-ops).

It's very hard to imagine RFC4361 being unsafe, considering its
simplicity.

But I have just had the opportunity to witness a "home network
appliance" containing a DHCP server which will reboot itself if
a "long" client identifier is provided (this was 25 bytes, partly
a hostname).

We haven't actually worked out how long a client identifier
it takes to...do whatever badness these things are doing
(sounds like a heap or stack overflow - very bad).

But I have to assume any value longer than 7 may produce unstable
results in appliances of either this or different manufacture.  That
is, that the behaviour of one kind of DHCP client in particular
(encoding a 7-byte hardware type and mac address string in the client
identifier) has become their expectation.  Design by sniffer: The rule
rather than the exception.

I have to imagine, speaking as a paranoid lunatic, there are going to
be other adoption pains along these lines (truncation at 7 bytes for
example...scary).

So that makes me question, as a client implementor, wether I should
send our customers headlong into this unknown forest (if I know
the DUID:IAID pairs we were to manufacture were to exceed 6 bytes in
length), or to make the adoption of RFC4361 user-optional.  A feature
you turn on rather than on-by-default.

I'm interested in other opinions.

-- 
ISC Training!  October 16-20, 2006, in the San Francisco Bay Area,
covering topics from DNS to DDNS & DHCP.  Email [email-masked].
-- 
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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