When a multicast forwarding entry (that is, an mroute) is added with an outgoing interface (OIF) on a port, the OIF count for that port is incremented. If you configure a port limit and the OIF count on the port count exceeds that limit, no OIFs on that port are added to mroutes (that is, new OIFs are blocked).
mroute port limit
- host1(config)#mroute port 3/0 limit 10