Re: Multipath (was: Re: Re-chartering for extension work)

[Christian Huitema <[e-mail]>]

On 12/16/2019 9:20 AM, Mikkel Fahnøe Jørgensen wrote:
> If you can observe encrypted traffic on both paths you have an
> opportunity to correlate traffic if an endpoint consistently acks on
> one path and sends on another. On path has small packets a fixed
> interval after larger packets on the other paths. That could happen in
> a migration scenario where one path is not yet fully committed so ACKs
> stay on the main path.
>
> I don’t recall how it works today with single path migration, but I
> think that it is required that ACKs happen on the same path as the
> packets on which they are sent.


No, that's not required. In fact it cannot be required, because one of
the scenarios is "transmit some data on path X, then migrate to path Y".
If you don't ack on path Y for packets sent on path X, you end up having
to repeat these packets on path Y.

But your general point is correct, Mikkel. If application traffic is
spread over multiple paths, it is probably hard to hide the correlation
between these multiple paths. Not necessarily impossible, but if this is
a goal we have better design for it.

-- Christian Huitema