RE: New Version Notification for draft-donley-ipv6-cpe-rtr-use-cases-and-reqs-00

["Chris Donley" <C.Donley@cablelabs.com>]

Regarding the link-local DAD failure on the WAN interface, we expect the
CPE router to use an EUI-64 address, and included a requirement for it
to "give up" if it detects a duplicate address to make the WAN-side
provisioning process more predictable. I think you're right that we
might want to be more graceful on the LAN side - we could clarify that
going forward.  

Regarding DHCPv6 DAD failure, we expect the device to send a DHCPv6
Decline, stop using the address, and restart the IPv6 provisioning
process, along the lines you suggest; however, we opted to remain silent
in this draft, in case vendors or operators have other ideas. Likewise,
we remained silent in the SLAAC case for similar reasons.

Chris


-----Original Message-----
From: Stark, Barbara [mailto:bs7652@att.com] 
Sent: Friday, July 10, 2009 1:49 PM
To: Jean-Francois.TremblayING@videotron.com
Cc: Chris Donley; v6ops@ops.ietf.org
Subject: RE: New Version Notification for
draft-donley-ipv6-cpe-rtr-use-cases-and-reqs-00

> For the DAD graceful failure, do you have any idea of what other
address could be used?
> Maybe if 2 DHCPv6 ADVERTISE were received from different servers,
another REQUEST could 
> be sent to the second server. Otherwise I don't see how we could make
the DAD failure 
> more graceful.

The draft only mentions DAD in relationship to the Link Local address
(4.1.2.1), so that's the usage I was commenting on. Presumably, DAD
would be used for all unicast addresses, before they're assigned to an
interface, consistent with RFC 4862. I hadn't really thought about what
to do if DAD fails on an address assigned via DHCPv6. That's kind of
weird. I suspect the CPE Router might do best to wait some interval and
try DHCPv6 again. Let the access network get its head on straight and
try to recover from whatever possessed it to do that.

For Link Local DAD failure, I haven't seen any precise suggestion for
exactly what to do. But RFC 4862 says if DAD fails, "If the address is
derived from an interface identifier, a new identifier will need to be
assigned to the interface, or all IP addresses for the interface will
need to be manually configured". I was hoping that vendors could play
around with figuring out some decent way to automatically assign a
different Interface ID for Link Local DAD failure on their CPE Routers.

The draft doesn't discuss or ask about SLAAC GUA DAD failure. I guess
that should be pretty easy for the CPE Router to just come up with
something different there, and try again.

I just don't think that single DAD failure on Link Local should
terminate that IPv6 interface. Multiple failures would be scary. Even
single failure shouldn't happen. But I don't think there's harm in
handling it gracefully. At least try a couple of times to assign a
different Interface ID automatically.
Barbara

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