Message 311658 - Python tracker

> Or the issue is specific for TCP_KEEPCNT for Windows only?

Four flags involved.
In this table, result column is search results from GitHub.

  keyword       available   result
TCP_FASTOPEN   win10 1607+   778
TCP_KEEPCNT    win10 1703+   3356
TCP_KEEPIDLE   win10 1709+   4820
TCP_KEEPINTVL  win10 1709+   3410

3.6 branch is using 1703 SDK, 3.7/3.8 branches are using 1709 SDK.

This discussion is beyond my knowledge, I keep watch.