[pkg-dhcp-devel] Bug#764219: isc-dhcp-client: fails to configure the default route

Ron ron at debian.org
Sun Oct 12 18:58:30 UTC 2014

Hi Scott,

On Sat, Oct 11, 2014 at 03:26:50PM +0100, Scott Ashcroft wrote:
> Hi,
> This isn't a bug in the dhcp client but a misconfiguration of your dhcp server.
> The 'DHCP Client Behavior' section of RFC3442 says, in part:
> "If the DHCP server returns both a Classless Static Routes option and
> a Router option, the DHCP client MUST ignore the Router option."
> So you just need to add the default route to your classless routes and
> everything will be fine.

Ah, thanks for the pointer to that.  I did consider putting the default
route into the classless list as a workaround if all else failed, but
I'd missed that not having it there was actually wrong.  When I couldn't
find any mention of this being a deliberate change the assumption became
"there's been an accident" and I stopped digging.

> I assume the previous version of dhcp client you were using either
> didn't support the classless routes or wasn't RFC compliant.

My understanding of this is the isc-dhcp-client has never supported this
as an 'intrinsic' option, but it's been supported in Debian for quite
some time now as a bolt-on option through use of an exit hook that sets
the routes.  Which is at least partly how I leapt to the conclusion
that something there got broken.

If the new version actually supports this beyond just ignoring the
Router option if it is present, then possibly the Debian patches for
that do still need to be looked at again too, and brought up to date
for it.  I'm only loosely familiar with this myself, and still don't
know exactly what changed related to this upstream yet.  A note that
it is a deliberate and new change in at least the Debian changelog
certainly wouldn't go astray in any case.

> I'll leave you to close the bug if you agree with my analysis.

Yeah, if the RFC is ambiguous about that, I'm not seeing it either.
I can confirm that putting the default route into the RFC3442 list
does appear to do the right thing with both Jessie and Wheezy DHCP
clients, at least for the configuration that I have.


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