[IPv6] Multi6 (no longer RFC 6724 shouldn't prefer partial reachability over reachability)

Brian E Carpenter <brian.e.carpenter@gmail.com> Wed, 22 November 2023 04:08 UTC

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Date: Wed, 22 Nov 2023 17:07:58 +1300
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To: Kyle Rose <krose@krose.org>, Ole Trøan <otroan@employees.org>
Cc: Michael Richardson <mcr+ietf@sandelman.ca>, 6man WG <ipv6@ietf.org>
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From: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Subject: [IPv6] Multi6 (no longer RFC 6724 shouldn't prefer partial reachability over reachability)
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On 22-Nov-23 06:31, Kyle Rose wrote:
> Someone help me out here, because I think I need a few blanks filled in with regard to MHMP.
> 
> When attempting to work through a straw man implementation, I ran into the problem that there is no way to signal to the client "use GUA from prefix A for default route X, and use GUA from prefix B for default route Y". 

That's why we did RFC 8028 "First-Hop Router Selection by Hosts in a Multi-Prefix Network", which requires rule 5.5 and only works with upstream SADR to find the correct exit.

    Brian

This implies that simply force-deprecating a prefix when a link goes down (setting preferred_lft to 0 in subsequent RAs) won't work because the up-up scenario would end up with clients arbitrarily using the wrong prefix for the wrong router.
> 
> Does that capture it? If so, that is solved by rule 5.5, so 5.5 should be made mandatory. But also, I am forced to agree with Ole that this is not a near-term solution. (Not that we shouldn't fix it, only that it won't immediately enable MHMP, so you'd need forwarding between routers to deal with the long tail of clients that don't upgrade.)
> 
> Kyle
> 
> 
> On Tue, Nov 21, 2023 at 12:06 PM Ole Trøan <otroan=40employees.org@dmarc.ietf.org <mailto:40employees.org@dmarc.ietf.org>> wrote:
> 
> 
> 
>>     On 21 Nov 2023, at 17:19, Ted Lemon <mellon@fugue.com <mailto:mellon@fugue.com>> wrote:
>>
>>     
>>     Indeed. And nobody is stopping anyone from offering it—I think we know how to do it. So I don't see a real issue here—we don't actually have to pick. What I'm reacting to is the apparent assertion that we shouldn't try to improve IPv6 stacks—that e.g. implementing rule 5.5 correctly is pointless. I don't agree with that.
>>
> 
>     Where exactly did I say that rule 5.5 was pointless?
> 
>     O.
> 
>>     On Tue, Nov 21, 2023 at 10:32 AM Ole Troan <otroan@employees.org <mailto:otroan@employees.org>> wrote:
>>
>>         Ted,
>>
>>         > Honestly, it feels to me like we are converging on something that works, and you are tired of it and are therefore proposing to snatch defeat from the jaws of victory.
>>         >
>>         > It’s taken a long time to do this because the market pressure isn’t there, not because it’s impossible to do.
>>
>>         It’s taken a long time for nothing to happen.
>>         Nothing has continued to happen.
>>
>>         There are millions of IPv6 nodes deployed.
>>         That’s not trivial to upgrade.
>>
>>         No, it’s not impossible to do. All the pieces to do it have been described for years.
>>         But just like SHIM6, ILNP, end to end IPsec, Multicast, IP Mobility, that doesn’t guarantee success.
>>
>>         Don’t know what kind of Herculean effort would be required. Interops and bakeoffs, IPv6 ready testing program, lots of guidance to application developers, new socket abstractions…
>>
>>         The other multi-homing mechanisms gives better (for some definition of) multi-homing with none of the host changes required.
>>
>>         Cheers,
>>         Ole
>>
>>
>>
>>
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