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Enable TCP Fast Open on Debian Jessie

Debian

According to TCP FAST OPENとは？ | REDBOX Labo, TCP Fast Open is supported on Linux since Kernel 3.6. The kernel of Debian Jessie is 3.16, so it is likely available.
The configuration value is /proc/sys/net/ipv4/tcp_fastopen. The value of my environment is 1.

root@c-021:~# cat /proc/sys/net/ipv4/tcp_fastopen
1
root@c-021:~#

The value means are described in this article. Summary is below.

  • 0: Disabled TFO
  • 1: Enable TFO when active connection only
  • 2: Enable TFO when passive connection only
  • 3: Enable TFO both active and passive connection

For more detail, include/net/tcp.h should be checked.