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 deprecated. 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.