4 # Both server and client-side TFO support must be enabled in the
5 # kernel, 'sudo sh -c "echo 3 > /proc/sys/net/ipv4/tcp_fastopen"'.
7 # A packet capture on the loopback interface will show the TFO
8 # option on the SYN, but the fast-output SMTP banner will not
9 # be seen unless you also deliberately emulate a long path:
10 # 'sudo tc qdisc add dev lo root netem delay 100ms'
12 # First time runs will see a TFO request option only; subsequent
13 # ones should see the TFO cookie and fast-output SMTP banner
14 # (currently on a separate packet after the server SYN,ACK but before
17 # The log <= line should have a "TFO" element.
19 # If the client-side is disabled in the kernel, Exim logs
23 # FreeBSD: it looks like you have to compile a custom kernel, with
24 # 'options TCP_RFC7413' in the config. Also set
25 # 'net.inet.tcp.fastopen.enabled=1' in /etc/sysctl.conf
28 exim -DSERVER=server -bd -oX PORT_D