TCP Fast Open (TFO)

Since Linux 3.6 (Client) and 3.7 (Server). (RFC 7413)

System Configuration

# 0 - disable
# 1 - enabled by clients (default)
# 2 - enabled by servers
# 3 - enabled by both of clients and servers
sysctl -w net.ipv4.tcp_fastopen = 3

echo 3 > /proc/sys/net/ipv4/tcp_fastopen

NGINX configuration

http {
    tcp_fastopen on;
}

server {
    listen 443 ssl fastopen=3;
}

Python Recipe

import socket

# Server
sock.setsockopt(socket.SOL_SOCKET, socket.TCP_FASTOPEN, 2)

# Client
sock.sendto(data, socket.MSG_FASTOPEN, addr)

`curl` Recipe

curl --tcp-fastopen <url>

References