# which might do the job. But how to manipulate it?
#
#
+# FreeBSD: it looks like you have to compile a custom kernel, with
+# 'options TCP_RFC7413' in the config. Also set
+# 'net.inet.tcp.fastopen.server_enable=1' in /etc/sysctl.conf
+# Seems to always claim TFO used by transport, if tried.
+#
sudo perl
system ("tc qdisc add dev lo root netem delay 50ms");
****
#
+#
+# Disable the TFO blackhole detection, as we seem to be running foul of it.
+# If bitten, we see the expected EINPROGRESS for sendto, yet no TFO cookie
+# option on the SYN.
+#
+sudo perl
+system ("[ -e /proc/sys/net/ipv4/tcp_fastopen_blackhole_timeout_sec ] && echo 0 > /proc/sys/net/ipv4/tcp_fastopen_blackhole_timeout_sec");
+****
+#
# First time runs will see a TFO request option only; subsequent
# ones should see the TFO cookie and fast-output SMTP banner
# (currently on a separate packet after the server SYN,ACK but before
#
#
#
-# FreeBSD: it looks like you have to compile a custom kernel, with
-# 'options TCP_RFC7413' in the config. Also set
-# 'net.inet.tcp.fastopen.enabled=1' in /etc/sysctl.conf
-# Untested.
-#
exim -DSERVER=server -bd -oX PORT_D
****
#
#
sudo perl
system ("tc qdisc delete dev lo root");
+system ("[ -e /proc/sys/net/ipv4/tcp_fastopen_blackhole_timeout_sec ] && echo 3600 > /proc/sys/net/ipv4/tcp_fastopen_blackhole_timeout_sec");
****
#
killdaemon