[Cake] [Codel] Proposing COBALT

[Eric Dumazet]

On Sat, 2016-06-04 at 22:55 +0300, Jonathan Morton wrote:
> > On 4 Jun, 2016, at 20:49, Eric Dumazet <eric.dumazet at gmail.com> wrote:
> > 
> > ECN (as in RFC 3168) is well known to be trivially exploited by peers
> > pretending to be ECN ready, but not reacting to feedbacks, only to let
> > their packets traverse congested hops with a lower drop probability.
> 
> In this case it is the sender cheating, not the receiver, nor the
> network.  ECN Nonce doesn’t apply, as it is designed to protect
> against the latter two forms of cheating (and in any case nobody ever
> deployed it).

Well, this is another demonstration of how ECN can be fooled, either by
malicious peers (senders and/or receivers), or simply bugs in TOS byte
remarking.

Senders (or a buggy router) can mark all packets with ECT(0), regardless
of ECN being negotiated at all in TCP 3WHS