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Opened 9 years ago

Closed 8 years ago

Last modified 7 years ago

#3001 closed enhancement (fixed)

Please enable ECN by default

Reported by: jch@… Owned by: developers
Priority: normal Milestone:
Component: base system Version:
Keywords: Cc:

Description

All Linux kernels since early 2.0 have had ECN support, but it is disabled by default.

ECN is a big win on wireless links, as it increases the likelihood of a TCP connection
reacting quickly after a link outage. ECN requires both host and router modifications,
and under Linux the router modification is only effective if the host modification is active.

  1. Host modification

Add the following to /etc/sysctl.conf:

net.ipv4.tcp_ecn=1

  1. Router modification

With the above change, the qos-scripts package will automatically enable ECN for all interfaces
with a red queuing discipline.

Ideally, a stock OpenWRT router would implement ECN, but this is difficult to do with current
Linux kernels, which can only do ECN with red.

Thanks for listening,

--Juliusz Chroboczek

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Change History (5)

comment:1 Changed 8 years ago by anonymous

Please *dont* enable ECN by default, but make it an option in the configuration files. The reason for this is that not every hop supports ECN, and this can cause hard to debug problems.

comment:2 follow-up: Changed 8 years ago by jch@…

Please *dont* enable ECN by default [...] not every hop supports ECN

Do you have any recent data to support this claim?

A number of broken firewalls used to corrupt ECN-enabled connections in the early 2000s. Most such problems have been fixed by now.

At any rate, enabling ECN on you OpenWRT boxen will not prevent non-ECN connections from going through them; it is only connections originating from them that will be ECN-enabled.

comment:3 Changed 8 years ago by nbd

  • Resolution set to fixed
  • Status changed from new to closed

enabled in r12334

comment:4 in reply to: ↑ 2 Changed 8 years ago by naf@…

Replying to jch@:

Please *dont* enable ECN by default [...] not every hop supports ECN

Do you have any recent data to support this claim?

For example on June 2008 packets with ECN bits was silently dropped at least by
www.vtb24.ru (large Russian bank) and www.gdeetotdom.ru (informational portal about real estate in Moscow).

...
At any rate, enabling ECN on you OpenWRT boxen will not prevent non-ECN connections from going through them; it is only connections originating from them that will be ECN-enabled.

... and will cause problems if OpenWRT box is used as a proxy.

comment:5 Changed 7 years ago by Patrick Goering <patrick_goering@…>

ECN enabled causes troubles for me too.

I have an OpenWRT box connected to a Sagem f@st 3202 (livebox) ADSL modem. The livebox drops all traffic with the ecn bit enabled. Thus anybody with this type of ADSL modem cannot connect anywhere from the OpenWRT box nor have anybody connect to the OpenWRT box.

Please disable ECN by default again like (almost?) all other operating systems do.

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