Index: share/man/man4/siftr.4
===================================================================
--- share/man/man4/siftr.4
+++ share/man/man4/siftr.4
@@ -131,6 +131,14 @@
 a particular log message, but calculating them adds additional computational
 overhead into the fast path.
 .El
+.Bl -tag -offset indent -width Va
+.It Va net.inet.siftr.port_filter
+controls on which source or destination port siftr should capture
+.Nm .
+By default, the value is set to 0, which means all ports are eligible for logging.
+Set to any other value, only packets where either the source or destination
+port is equal to this number are logged.
+.El
 .Ss Log Format
 A typical
 .Nm
Index: sys/netinet/siftr.c
===================================================================
--- sys/netinet/siftr.c
+++ sys/netinet/siftr.c
@@ -919,8 +919,8 @@
 	 * can be inserted into the pkt_queue
 	 */
 	if ((siftr_port_filter != 0) && 
-	    (siftr_port_filter != ntohs(inp->inp_lport)) &&
-	    (siftr_port_filter != ntohs(inp->inp_fport))) {
+	    !((siftr_port_filter == ntohs(inp->inp_lport)) ||
+	    (siftr_port_filter == ntohs(inp->inp_fport)))) {
 		goto inp_unlock;
 	}
 
@@ -1104,8 +1104,8 @@
 	 * can be inserted into the pkt_queue
 	 */
 	if ((siftr_port_filter != 0) && 
-	    (siftr_port_filter != ntohs(inp->inp_lport)) &&
-	    (siftr_port_filter != ntohs(inp->inp_fport))) {
+	    !((siftr_port_filter == ntohs(inp->inp_lport)) ||
+	    (siftr_port_filter == ntohs(inp->inp_fport)))) {
 		goto inp_unlock6;
 	}