Re: [multipathtcp] 6824bis -11 review

[Yoshifumi Nishida <[e-mail]>]

On Tue, Jul 31, 2018 at 5:07 AM, Alan Ford <[e-mail]> wrote:

> Hi Rahul, all,
>
>
> On 31 Jul 2018, at 01:21, Rahul Arvind Jadhav <[e-mail]>
> wrote:
>
> c) sending a new ADD_ADDR with same ID + address and different port is fine
> [RJ] again this is what the text already says, but I’m not still clear
> about this. Why ID + address has to match? Only ID should be enough.
>
> Consider:
>
> a) ADD_ADDR comes in saying ID=2, addr=10.0.0.1 (private)
> b) MP_JOIN comes in saying ID=2, addr=8.9.10.11 (public)
> c) ADD_ADDR comes in saying ID=2, addr=192.168.0.1
>
> What does this mean? Is (c) an implicit REMOVE+ADD? And thus does this
> mean the subflow created in (b) is now no longer valid?
>
> By keeping the address / ID mapping, if an address is lost, then so is the
> subflow.
>
> [RJ2] Rather than viewing ( c) as an implicit REMOVE+ADD, can we see it as
> an UPDATE? Because ID remains same. Subflow created in (b) remains valid
> (not sure if I’m missing anything here, I see no reason to lose this
> subflow).
> In step ( c), the receiver can override Address field in context to ID=2
> to the new addr (192.168.0.1) ……   8.9.10.11 is kept separately as the
> learnt actual rcvd IP (from MP_JOIN) in the same context ID=2. We have to
> agree that an implementation needs to maintain this IP separately in
> context to ID=2 anyways.
> So if we do an explicit REMOVE+ADD, the end result is the same as this
> UPDATE (but with much less overhead & impl ease).
>
>
> I would be interested in hearing from other implementers here… Is there an
> issue with “updating” using ADD_ADDR?
>
> Given we say that REMOVE_ADDR should not remove a subflow if it’s still
> alive, we have precedent for implying a subflow can exist to an address
> which does not have an Address ID - to - IP address mapping.
>
> So given that, does updating, as Rahul suggests, cause a problem?
>
>
Hmm.. I am wondering why we want to re-use the same address ID while we
have 0-255 values for it?
Do we have some advantage for it? I thought picking up a new ID would be
safer and simpler..
As Alan mentioned, when we try to "update" the address ID, we will have to
keep both addresses until we confirm that old one is not used anymore.
Also, in the case described above, what will happen if (b) was delayed and
arrived after (c)?

Thanks,
--
Yoshi