dhclient didn't wait for dhcpoffer

David W. Hankins dhankins at isc.org
Fri Jun 5 21:37:16 UTC 2009

On Tue, Jun 02, 2009 at 01:47:38PM -0700, Jeff Haran wrote:
> Beats me why a DHCP server would offer this in the first place though.
> This address range is intended for nets without DHCP servers.

one of the things that RFC 2131 specifies is that the client is to
wait a period after receiving its first offer and acting on it - on
the basis that there may be multiple offers and it should select the
'best'.  isc dhclient does this by default, but most people disable
it because we don't have a selection algorithm.  we still wind up
using the first offer anyway, so there's no practical benefit.

this selection process is not really very well defined (3315 is
better, but it is incomplete, requiring the implementor to use their
imagination), and that is a problem because that selection process is
an externally visible behaviour.

it would be good if there were a formally defined selection process,
and i think 'offered address matches the following masks...' should
be in there somewhere.

we should also be sorting globally routed addresses ahead of rfc1918
space, for example, when judging between multiple offers.

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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