Re: graceful renumbering of CPE networks

Mikael Abrahamsson <swmike@swm.pp.se> Tue, 26 February 2019 13:20 UTC

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Date: Tue, 26 Feb 2019 14:20:22 +0100
From: Mikael Abrahamsson <swmike@swm.pp.se>
To: Michael Richardson <mcr+ietf@sandelman.ca>
cc: Brian E Carpenter <brian.e.carpenter@gmail.com>, 6man WG <ipv6@ietf.org>
Subject: Re: graceful renumbering of CPE networks
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On Sun, 24 Feb 2019, Michael Richardson wrote:

> The part that is missing is some kind of "push" notification from the 
> ISP to the CPE that new addresses are available.  That need not obsolete 
> the old addresses --- the lifetime contract can be maintained. Probably 
> such a thing could be simulated by adjustment of T1 and T2 timers in 
> DHCP-PD, forcing the CPE to come back to confirm the old address, and at 
> that point, adding the new prefix.  This may require new specification 
> as well as new code; those parts of DHCP are not in my brain cache right 
> now.

This is an interesting idea.

In the context of 
https://datatracker.ietf.org/doc/draft-patterson-intarea-ipoe-health/ 
we've been looking for what could make the HGW refresh its view of the 
world towards the ISP. It would be beneficial if the ISP router also could 
signal to the HGW that "hey, I just restarted, please reconfirm your 
beliefs". This would by design be cross-protocol and this message needs to 
affect both DHCP and SLAAC for instance.

We also of course need to make it less likely that there is all of a 
sudden a request storm, so some kind of exponential backoff would be 
needed.

What do we already have that could be used for this? Some kind of option 
to stick into an RA for the first few minutes after up:ing a new 
interface? An uptime counter to stick into the RA, and if it goes 
backwards then re-confirm? What's the least change possible for all 
involved entities to achieve that?

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se