Subject: [multipathtcp] Multipath TCP Address advertisement 5/5 - Communities

From: Fabien Duchêne <[email-masked]>
Date: Sun, 6 Nov 2016 13:38:22 +0100

Hello,

As we agreed in Berlin during IETF96, here are a few email to discuss
the contributions proposed in
https://datatracker.ietf.org/doc/draft-duchene-mptcp-add-addr/

To allow a host to inform the receiving host about the diversity of
several addresses we propose to modify the ADD_ADDR to include 4 bits
describing a "Community" associated to this address.
The community values are an opaque field and it is expected that two
addresses having the same community share some resources.

With the community bits, a dual-stack host could elect to regroup all
the addresses attached to a single interface under the same community,
allowing the receiving host to decide on which advertised addresses it
wants to establish new subflows.
This is because in the case of a dual-stack host, establishing v4 and V6
subflows
is not always the best solution.
The idea here is to design a generic solution to regroup the address
that shares
the same forwarding type in a specific class.

Fabien

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From: Christoph Paasch <[email-masked]>
Date: Sat, 12 Nov 2016 23:53:27 -0800

Hello,

> the same forwarding type in a specific class.

I support this. Although, I wonder whether we need to use 4 bits. Maybe 3
are enough? (just trying to spare a bit ;))

Christoph

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From: Fabien Duchêne <[email-masked]>
Date: Mon, 14 Nov 2016 02:32:29 +0100

Hello,

inline

> are enough? (just trying to spare a bit ;))
Hum, why not? I didn't really think about that while writing the draft, 
it was more "all your bits are belong to us" :D
8 values seems more than enough to me!

Fabien

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From: Alan Ford <[email-masked]>
Date: Mon, 14 Nov 2016 07:05:42 +0000

Hi all,

After discussion at IETF97, I do not support this proposal. I can’t see any scenarios where this would actually be particularly useful.

Specifically, no end host really has enough knowledge to say their IPv4 and IPv6 addresses go over the same path, other than they share the same physical interface at an end host. Some ends may have a good idea, e.g. data centres.

But if you as a server know your IPv6 and IPv4 share a path, you may choose not to use one or the other. Same for the client. So under what circumstances does signalling this to the far end actually help?

Regards,
Alan

> On 6 Nov 2016, at 12:38, Fabien Duchêne <[email-masked]> wrote:
> 
> Hello,
> 
> _______________________________________________
> multipathtcp mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/multipathtcp

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From: Fabien Duchêne <[email-masked]>
Date: Mon, 14 Nov 2016 16:09:50 +0900

> But if you as a server know your IPv6 and IPv4 share a path, you may choose not to use one or the other. Same for the client. So under what circumstances does signalling this to the far end actuall…
mm thinking about it:
let's say that you have a v4 and a v6 that share a path, so you don't 
announce the v6. What happen if the v4 fails if you didn't announce your v6?

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From: Alan Ford <[email-masked]>
Date: Mon, 14 Nov 2016 07:28:59 +0000

You could advertise it with your ‘backup’ bit in proposal 3/5 :-)

> On 14 Nov 2016, at 07:09, Fabien Duchêne <[email-masked]> wrote:
> 
> 
> 
> let's say that you have a v4 and a v6 that share a path, so you don't announce the v6. What happen if the v4 fails if you didn't announce your v6?
>> 
>> Regards,
>> Alan
>> 
>

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From: Fabien Duchêne <[email-masked]>
Date: Mon, 14 Nov 2016 16:49:58 +0900

Yep, that was my first thought, now the thing that bothers me here is 
the following:

You have 2 interfaces. Each does have v4 and v6 (like a lot of 
smartphones today).
So you use the v4's and advertise the v6's with the backup bit from 
proposal 3.

One of the v4 breaks, now you have 2 v6s that you could "unbackup" but 
which one do you "unbackup"?
You don't know which v6 is related to the v4 you just lost.

Fabien

On 11/14/2016 04:28 PM, Alan Ford wrote:
> You could advertise it with your ‘backup’ bit in proposal 3/5

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From: Fabien Duchêne <[email-masked]>
Date: Mon, 14 Nov 2016 16:51:06 +0900

> You could advertise it with your ‘backup’ bit in proposal 3/5 :-)
On a lighter note: are you saying that you're supporting the proposal 
3/5 ? :)

Fabien