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Understanding Layer 3 Multicast Functionality on the SRX5K-MPC

Multicast is a “one source, many destinations” method of traffic distribution, meaning that only the destinations that explicitly indicate their need to receive the information from a particular source receive the traffic stream.

In the data plane of the SRX Series chassis, the SRX5000 line Module Port Concentrator (SRX5K-MPC) forwards Layer 3 IP multicast data packets, which include multicast protocol packets (for example, MLD, IGMP and PIM packets), and the data packets.

In incoming direction, the MPC receives multicast packets from an interface and forwards them to the central point or to a Services Processing Unit (SPU). The SPU performs multicast route lookup, flow-based security check, and packet replication.

In outgoing direction, the MPC receives copies of a multicast packet or Layer 3 multicast control protocol packets from SPU, and transmits them to either multicast capable routers or to hosts in a multicast group.

In the SRX Series chassis, the SPU perform multicast route lookup, if available, to forward an incoming multicast packet and replicates it for each multicast outgoing interface. After receiving replicated multicast packets and their corresponding outgoing interface information from the SPU, the MPC transmits these packets to next hops.


On all SRX Series devices, during RG1 failover with multicast traffic and high number of multicast sessions, the failover delay is from 90 through 120 seconds for traffic to resume on the secondary node. The delay of 90 through 120 seconds is only for the first failover. For subsequent failovers, the traffic resumes within 8 through 18 seconds.