[PATCH RFC v2 0/3] dhclient: add --prefix-len option

H. Peter Anvin hpa at zytor.com
Wed Dec 2 22:00:48 UTC 2015

On 12/02/2015 01:53 PM, Shawn Routhier wrote:
>> On Dec 2, 2015, at 1:46 PM, H. Peter Anvin <hpa at zytor.com> wrote:
>> On 12/02/2015 12:47 PM, Shawn Routhier wrote:
>>> I merged them last night (my time - US PT) so it would depend on when you
>>> did the pull.  I haven’t reviewed your changes yet so it’s possible that there
>>> aren’t issues, but given the quick look I did on the first patch I think you would
>>> have noticed.
>> Yes, in fact looks like we implemented several similar things although
>> in slightly different ways.  Unfortunate timing.  I will try to update
>> the patchset as soon as possible.
> We are about half way through a release cycle.  I’m not sure if we
> would get your patch into the next release or not.  We would definitely
> put it into our bug system so it wouldn’t get lost.

For what it's worth, I have run the original version of this patch
(before I did the refactoring) for almost three years on a Comcast
network, so it is at least not *completely* bogus :)

>> RFC 7550 seems to imply that unsatisfied prefix requests should be
>> repeated in at least a REBIND message, possibly a REQUEST message too?
>> 	-hpa
> yes, my patch should do that.

Sure, but if we get an IA_PD delegation for 2001:db8:1234:5678::/64 when
what we want is a /56, I believe we should include the ::/56 request
again in those messages, too, in addition to repeating the
2001:db8:1234:5678::/64 prefix.  My patch currently would drop the
too-narrow /64 prefix from a SOLICIT message, however.

> there is also a change to the scoring algorithm to choose leases
> from different servers (if you actually have two or more dhcp servers
> to choose from).  The new scoring prefers more bindings over more
> addresses.  So a lease with an IA_NA and IA_PD with one address (prefix)
> each is preferred over a lease with an IA_NA with two addresses.

We should also penalize the scoring of an IA_PD with a longer prefix
than we asked for, so if one server offers us a /60 and one a /64 when
we wanted a /56, we would pick the /60.


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