Re: [v6ops] A common problem with SLAAC in "renumbering" scenarios

Fernando Gont <fgont@si6networks.com> Sun, 03 February 2019 09:43 UTC

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To: Mikael Abrahamsson <swmike@swm.pp.se>
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From: Fernando Gont <fgont@si6networks.com>
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Date: Sun, 03 Feb 2019 02:17:50 -0300
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Subject: Re: [v6ops] A common problem with SLAAC in "renumbering" scenarios
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On 1/2/19 16:02, Mikael Abrahamsson wrote:
> On Thu, 31 Jan 2019, Fernando Gont wrote:
> 
>> Question:
>> How about making the update to the "Valid Lifetime" a SHOULD or MAY,
>> instead?  Or, maybe, at least, set it to the current "Valid Lifetime"?
>> Otherwise, with the default values for the "Valid Lifetime", the
>> addresses might lie around for 1 month....
> 
> I had a real life example today. I have OpenWrt 18.06.1 HGW. This
> morning, I lost Internet access. After diagnosing I realised that WAN
> was not working correctly, so I did "ifdown wan" and "ifdown wan6",
> switched to my secondary provider (which I was still on contract with
> but don't normally use) and then did "ifup" on both. I received new IPv4
> GUA and IPv6 GUA PD /56, which was then announced on my br-lan. I then
> ran on that for 3-4 hours until my regular provider had fixed their
> hardware problem. Then I did the whole ifddown procedure, swapped WAN
> cable to normal ISP, and did ifup again.
> 
> Now, I saw IPv6 IA_NA for the temp ISP /56 with a week lifetime on wired
> LAN device so I was a bit worried this would cause long-time problems,
> but the prefixes were deprecated and I couldn't find any actual issues
> (source address selection worked properly). A few hours later all these
> addresses were gone even from my purely wired devices that hadn't seen
> any link down/up events.
> 
> So potentially RFC7084 style solves most problems together with
> https://tools.ietf.org/html/draft-patterson-intarea-ipoe-health-05 style
> WAN down/up detection for the IPoE deployment case (PPPoE already have
> this).

This is a different problem scenario: the router is in an easy position
to clean up after itself, whereas in the case of crash-and-reboot most
aren't (since most don't record the prefix they were advertising).



> OpenWrt since 15.05 has been very much aimed to be RFC7084 compatible so
> I would propose to investigate further what hosts today actually do in
> reaction to RFC7084 signalling.

What do you mean by "RFC7084 signaling"?

Thanks!

Cheers,
-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492