On Tue, Jun 30, 2020 at 1:44 PM David Miller [off-list ref] wrote:

From: Eric Dumazet <edumazet@google.com>
Date: Tue, 30 Jun 2020 13:39:27 -0700

quoted

The (C) & (B) case are certainly doable.

A) case is more complex, I have no idea of breakages of various TCP
stacks if a flow got SACK
at some point (in 3WHS) but suddenly becomes Reno.

I agree that C and B are the easiest to implement without having to
add complicated code to handle various negotiated TCP option
scenerios.

It does seem to be that some entities do A, or did I misread your
behavioral analysis of various implementations Mathieu?

Thanks.

Yes, another question about Mathieu cases is do determine the behavior
of all these stacks vs :
SACK option
TCP TS option.