[Bloat] tcp_ecn=2 (server-mode ECN)

["Henrique de Moraes Holschuh" <hmh@hmh.eng.br>]

On Wed, 13 Apr 2011 22:44 -0600, "Dave Taht" <d@taht.net> wrote:
> He'd not noticed the problem because ubuntu 10.4 (at least, he also
> runs bsd) has tcp_ecn=2, which so far as I know "tries" a ECN enabled
> connect then falls back to not using it.

tcp_ecn=2 is "server mode ECN".  It will enable ECN if, and ONLY if, the
other side requests it during the initial TCP handshake.

AFAICT, it effectively disables ECN on all outgoing connections and
enables it on incoming connections should the other host request ECN
(which it won't when it is also running in tcp_ecn=2 mode).

It is also the kernel default, and AFAIK, the default on every 2010+
Linux distro stable releases.

If you want to use ECN, you have to set tcp_ecn=1 in your Linux box when
you're the one originating TCP connections.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh