[Mailman-Users] ECN (Explicit Congestion Notification) Problem with 'www.list.org'

enyc at mail.evtech.org enyc at mail.evtech.org
Thu Feb 10 19:54:15 CET 2005

The services for the host on 


[all the same host/machine]
Including "list.org" SMTP and "www.list.org" HTTP --

Appear to be affected by a 'faulty router or firewall' of some form, that
  THROWS AWAY "TCP SYN" packets trying to connect to the machine if the
  'ECN bits' (previously 'reserved for future use') are set on the TCP
  packet.  This problem most affects Linux users as the Linux 2.4 / 2.6
  enable "ECN" (explicit congestion notification) by-default and do not
  provide a "fallback mechanism" like some BSD systems do!
I.e. such systems will TOTALLY FAIL to connect to such a host.

Hosts that do not understand "ECN" are supposed to merely ignore these
  bits and carry-on-working-as-usual like the vast majority of hosts

Many distributions disable ECN at boot-time to work around such broken
  hosts which are decreasingly-common.

Please see  http://www.icir.org/floyd/ecnProblems.html
  for more information and links.

--"enyc" <enyc at mail.evtech.org>

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