+This allows you to match the ECN bits of the IPv4 and TCP header. ECN is the Explicit Congestion Notification mechanism as specified in RFC3168
+.TP
+.BI "--ecn-tcp-cwr"
+This matches if the TCP ECN CWR (Congestion Window Received) bit is set.
+.TP
+.BI "--ecn-tcp-ece"
+This matches if the TCP ECN ECE (ECN Echo) bit is set.
+.TP
+.BI "--ecn-ip-ect " "num"
+This matches a particular IPv4 ECT (ECN-Capable Transport). You have to specify
+a number between `0' and `3'.