Cisco Systems 6500, EA6500 Non-RPF Traffic Processing

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Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E

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Chapter 18 Configuring IP Multicast Layer 3 Switching

Understanding How IP Multicast Layer 3 Switching Works

In PFC2 systems, (*,G) flows will be partially switched on the last-hop leaf router if the shared-tree to

shortest-path-tree (SPT) threshold is not equal to infinit y. This allows the flow to transition from SPT.

Note With a PFC2, flows matching an output ACL on an outgoing interface are routed in software.

When all the outgoing Layer 3 interfaces for a given flow are Layer 3 switched, and none of the above

situations apply to the flow, that flow is considered completely switched. When a completely switched

flow is created, the PFC prevents multicast traffic bridged on the source VLAN for that flow from

reaching the MSFC interface in that VLAN, freeing the MSFC of the forwarding and replication load for

that flow.

One consequence of a completely switched flow is that multicast statistics on a per-packet basis for that

flow cannot be recorded. Therefore, the PFC periodically sends multicast packet and byte count statistics

for all completely switched flows to the MSFC. The MSFC updates the corresponding multicast routing

table entry and resets the expiration timer for that multicast route.

Note A (*,G) state is created on the PIM-RP or for PIM-dense mode but is not used for forwarding the flows,

and Layer 3 switching entries are not created for these flows.

Non-RPF Traffic Processing

These sections describe non-RPF traffic processing:

• Non-RPF Traffic Overview, page 18-5

• Filtering of RPF Failures for Stub Networks, page 18-6

• Rate Limiting of RPF Failure Traffic, page 18-6

In a redundant configuration where multiple routers connect to the same LAN segment, only one router

forwards the multicast traffic from the source to the receivers on the outgoing interfaces (see

Figure 18-1). In this kind of topology, only the PIM designated router (PIM DR) forwards the data in the

common VLAN, but the non-PIM DR receives the forwarded multicast traffic. The redundant router

(non-PIM DR) must drop this traffic because it has arrived on the wrong interface and fails the RPF

check. Traffic that fails the RPF check is called non-RPF traffic.

The Catalyst 6500 series switch pr ocesses no n-RPF traffic in hardware on the PFC by filtering (dropping)

or rate limiting the non-RPF traffic.