Subject: Re: [dhcwg] RFC 3315 - Dhcpv6 client message retransmission question

From: "David W. Hankins" <[email-masked]>
Date: Tue, 17 Nov 2009 16:44:09 -0800

On Wed, Oct 21, 2009 at 04:37:10PM +0200, Bud Millwood wrote:
> Out of curiosity, why was +-0.1 chosen over DHCPv4's +-1.0 for each 
> re-transmission? This is less spread with higher peak volume - what was the 
> motivation for it?

I don't know why the DHCPv6 way was selected over the DHCPv4 way, but
as an implementer of both I'll say DHCPv6's is simpler to implement.

As we've never had as serious a problem in DHCPv4 with clients that
do some kind of random backoff (even mis-implemented ones) than we
have had with clients that do no random backoff, simpler is provably
better.

With our current mix of DHCPv4 client implementation, even wide area
blackouts have not had a meaningful impact on DHCPv4 server
operations.  It turns out that clients are sufficiently heterogeneous
that they have slightly different startup times between applying power
to a power-grid sized area and starting to send their first
DHCPDISCOVER packets; they don't even all flood at the same time.  And
power grids don't all get turned on at the same time; they are
generally brought online one at a time even when their re-commission
isn't dictated by hardware replacements (in the northern Virginia
freeze of 1999 (?), power was restored to parts within the many
affected power-grid sized areas over the course of several days, as
the freeze had caused local communities' transformers to blow and had
to be replaced).

So even in large scale coordinated restarts, clients trickle in to
start with.

Even if you did have a homogeneous population of clients in a power
grid sized area flood the server all at once, generally customers are
much happier that the heat, oven, fridge, or air conditioning are back
on than to be bothered to wonder why you don't have Internet access in
millisecond scale.

> > I guess you're predicting that DHCPv6 will hit the big time in 2012?
> 
> OK... it's a prediction. Maybe we should start a pool. :)

No, you should write a draft to fix it.

Clearly what we need is a DHCPv6 option that assigns Armageddon fates
to the users (you 3 thousand report to escape ship 5, you 300 thousand
will make a human sandbag trap for the flows of lava to ensure time
for the first group's liftoff...), so humanity can quickly and
efficiently mobilize to make sure DHC is preserved off-world.

Probably this option would be a real driver for IPv6 uptake (as the
alternative is to be assigned default fate; to wander the Earth's
post-apocalyptic, barren wastelands alone).  Either that, or it would
be a sure way for us to get rid of those annoying IPv6 people and
finally get the planet to ourselves.

-- 
David W. Hankins	BIND 10 needs more DHCP voices.
Software Engineer		There just aren't enough in our heads.
Internet Systems Consortium, Inc.		http://bind10.isc.org/