4 ms·

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

by obtu 14y ago

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_Notification#ECN_support_in_TCP_by_hosts https://en.wikipedia.org/wiki/Explicit_Congestion_Notificati...

pepijndevos 14y ago
Any ideas about XP? My brother is having trouble playing quake on his XP while I download Ubuntu images on my Mac.
- obtu 14y ago
  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.
woodrow 14y ago
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 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.
nzmsv 14y ago
Interesting. I just enabled this on my machines. Is there a way to find out whether ECN has been successfully negotiated?
- obtu 14y ago
  I don't see it in netstat -s. Possibly you'd have to hack up a netfilter rule.
  - obtu 14y ago
    Or you can test negotiation towards a particular host using this patched scamper, a traceroute-like tool: http://test-ecn.csail.mit.edu/ http://test-ecn.csail.mit.edu/

by obtu 14y ago

pepijndevos 14y ago

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

obtu 14y ago
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.

woodrow 14y ago

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 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.

nzmsv 14y ago

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

obtu 14y ago
I don't see it in netstat -s. Possibly you'd have to hack up a netfilter rule.
- obtu 14y ago
  Or you can test negotiation towards a particular host using this patched scamper, a traceroute-like tool: http://test-ecn.csail.mit.edu/ http://test-ecn.csail.mit.edu/