--- /dev/null
+This matches the routing realm. Routing realms are used in complex routing
+setups involving dynamic routing protocols like BGP.
+.TP
+[\fB!\fP] \fB--realm\fP \fIvalue\fP[\fB/\fP\fImask\fP]
+Matches a given realm number (and optionally mask). If not a number, value
+can be a named realm from /etc/iproute2/rt_realms (mask can not be used in
+that case).