Windows Tips

Enable Compound TCP

Compound TCP is a Hybrid TCP Congestion Control approach. You can also enable ECN (lossless congestion control feedback):

If enough end users enable ECN, core providers may be inclined to deploy AQM with Packet Marking too… And as Home Gateways are those which are prone to ECN implementation bugs, a full disconnect from the internet (rather than certain sites not reachable) is quite easy to quickly diagnose.

Also, enabling ECN gives you more retries with the SYN (3x ECN+SYN, 3x normal SYN), so in a heavy congested / bufferbloated environment, your small flows might get through eventually, with higher probability.

Windows Vista / Windows 7 users can enable “Compound TCP”,

netsh int tcp set global congestionprovider=ctcp
netsh int tcp set global ecncapability=enabled

Windows 8

The use of netsh int tcp set global congestionprovider=ctcp has been depreciated. In order to set or change the congestionprovider the following command must be used:

set-nettcpsetting -CongestionProvider CTCP

However, CTCP is the default on windows 8 and later. Changing the setting does not seem to work on Windows 10.

Type get-nettcpsetting to view other settings that used to be part of netsh tcp global.

ECN is a global setting and is still configurable, even on clients, through netsh by running:

netsh int tcp set global ecn=enable

On Windows Server 2012, you can change this setting through the custom template or netsh.

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Recent News & Articles

Mar 21, 2019 Wiki page
Dave Taht's Take on TCP
Mar 17, 2019 Wiki page
Jake Holland's Stance on ECN
Sep 6, 2018 Wiki page
Pete Heist's Thoughts on ECN
Sep 5, 2018 Wiki page
Dave Taht's Stance on ECN
Sep 4, 2018 Wiki page
Jonathan Morton's Take on ECN

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