ap/app/iptables/extensions/libipt_ECN.man

This target allows to selectively work around known ECN blackholes.
It can only be used in the mangle table.
.TP
\fB\-\-ecn\-tcp\-remove\fP
Remove all ECN bits from the TCP header.  Of course, it can only be used
in conjunction with
\fB\-p tcp\fP.