Re: [v6ops] SLAAC renum: Problem Statement & Operational workarounds

Fernando Gont <> Thu, 24 October 2019 11:18 UTC

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To: Philip Homburg <>,
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From: Fernando Gont <>
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Subject: Re: [v6ops] SLAAC renum: Problem Statement & Operational workarounds
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Hello, Philip,

On 24/10/19 02:42, Philip Homburg wrote:
>> A better mitigation is to affect the preferred and possibly the valid
>> lifetimes in response to consecutive RAs from the same router that lack
>> the original (stale) prefix. e.g., after two consecutive RAs that do not
>> contain the existing prefix, reduce the preferred lifetime. After two
>> additional RAs, reduce the valid lifetime.
> I think that to avoid confusion it is probably best to have 3 documents:
> - one that describes host behavior. I think that what you describe above would
>   fit in such a document. There is a lot we can do to make hosts more robust.

Agreed. FWIW, We should have such document ready this weekend.

> - one that describes CPE behavior. If the CPE explicitly deprecates old
>   prefixes then that solves the problem with CPE reboots. Having
>   more sensible lifetimes fits in such a document, but I don't think it
>   provides a solution. It just reduces some secondary effects such as
>   stale prefix build up.


> - Finally, a document for ISPs describing how to best provide prefixes 
>   using DHCPv6-PD. 
> I think all 3 approaches are needed:
> - a host doesn't want to rely on a cheap CPE doing its job.
> - a quality CPE can provide better support for hosts today. There will always
>   be ISPs that do flash renumbering
> - finally a quality ISP may have a need to renumber customers and would like
>   to do so without breaking things.

I fully agree with your assessment. That said, maybe the first step is
to start with a problem statement, as with this document?


Fernando Gont
SI6 Networks
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