Multicast Routing Table Preferences Overview
You can configure the following settings for the multicast routing table:
Enable Multiple Incoming Interfaces—Select this option to permit multiple routes with different incoming interfaces for the same source and multicast group.
Maximum Entries—Enter the maximum number of route entries you want the multicast routing table to hold. By default, this option is set to 4096.
Negative Mroute Cache—Select this option to store unrouteable multicast packets in a cache until a multicast route can be established for the packet. For example, the security device might be unable to immediately route a multicast packet when:
The IGMP proxy receives a data packet for which it has no interested member. The device creates a negative mroute entry for the packet and stores the packet in the negative mroute cache. When the IGMP proxy receives a group join for the source (or source and group), the device automatically forwards the cached packet.
The device receives a data packet from a locally connected PIM-SM but does not have a group RP mapping for that group. The device creates a negative mroute entry for the packet and stores the packet in the negative mroute cache. When the device learns the RP mapping, it automatically registers and forwards the packet.
In an active-active NSRP configuration, the device that is not responsible for forwarding packets receives a multicast data packet. The device creates a negative mroute entry for the packet and stores the packet in the negative mroute cache. When the device that is responsible for forwarding packets learns of the group interest for the data packet, it forwards the packet.
When you enable Negative Mroute Cache, you can also configure a timer that controls how the device ages unrouteable packets in the cache. By default, the timer is set to 90 seconds, meaning that the device deletes a route entry in the cache after 90 seconds. The acceptable range is 10 to 180 seconds.