Subject: [dhcwg] Vista, DHCPv4, broadcast bit

From: "David W. Hankins" <[email-masked]>
Date: Wed, 19 Sep 2007 15:27:38 -0700

Apologies if (I think) Ralph asked this question a few months ago?
Google can't seem to find it in the archives.

Is anyone familiar with the Windows Vista DHCPv4 client able to tell
me why it sets the broadcast bit on by default, but also supplies a
registry key to turn the behaviour off?

  http://support.microsoft.com/kb/928233/en-us

RFC1542 section 3.1.1 seems to me to be saying that this flag is meant
to advertise capability, not preference.  If a client is capable of
receiving unicasts, it really should clear the bit.

It's not causing any protocol level interoperability problems that I'm
aware of - but it is causing operational problems.

It appears that some networks have actually become accustomed to
carrying nothing but unicast DHCPv4 traffic, and are just now finding
problems with broadcast traffic now that it's appeared with Vista.

  http://slashdot.org/article.pl?sid=07/09/02/1223209
  http://marc.info/?l=dhcp-users&m=119014501022864&w=2

Idle paths suddenly excercised.

My own interest is in clarifying DHCPv4 protocol.  If there are
motivations to set the bit outside of client capability that outweigh
the concerns that increased broadcasts represent, we should document
them.

-- 
Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
-- 
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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