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Comment by obtu | Hacker News Reader

Huh, I wasn't aware ECN wasn't enabled everywhere yet.

To enable it on Linux:

    sudo sysctl net.ipv4.tcp_ecn=1

Across reboots:

    echo net.ipv4.tcp_ecn=1 |sudo tee /etc/sysctl.d/10-ecn.conf

Other OSes: https://en.wikipedia.org/wiki/Explicit_Congestion_Notificati...

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It's difficult to take advantage of ECN nowadays, too. Some ISPs seem to clobber the ECN field when packets enter their AS. This is measured and discussed here: http://dl.acm.org/citation.cfm?id=2068833. Notably:

"""Via large-scale path measurements, we find the ECN feedback loop failing in the core of the network 40% of the time, typically at AS boundaries."""

So, unfortunately, we've got a ways to go on this.

Interesting. I just enabled this on my machines. Is there a way to find out whether ECN has been successfully negotiated?

I don't see it in netstat -s.

Possibly you'd have to hack up a netfilter rule.

Or you can test negotiation towards a particular host using this patched scamper, a traceroute-like tool: http://test-ecn.csail.mit.edu/

Any ideas about XP? My brother is having trouble playing quake on his XP while I download Ubuntu images on my Mac.

There's nothing the XP computer can do to fix that, as it is the victim of the delays and needs the cooperation of other hosts that are to some degree involved in causing the problem. As I understand it, ECN on the Mac enables the Mac to cooperate with queue management elsewhere (the Mac could be doing its own queue management without ECN, but probably doesn't). The Quake trouble indicates the bottleneck is an overlarge buffer on a router you both share. You need your shared router to do some queue management (CeroWrt is a good platform for this) so that large downloads don't increase delays for all connections. If your ISP modem has bloated buffers and you can't replace it, you may be entirely out of luck.

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