User Guide

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Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
78-14099-04
Chapter 18 Configuring IP Multicast Layer 3 Switching
Understanding How IP Multicast Layer 3 Switching Works
Figure 18-1 Redundant Multicast Router Configuration in a Stub Network
Filtering of RPF Failures for Stub Networks
PFC1, PFC2, and the DFCs support ACL-based filtering of RPF failures for sparse mode stub networks.
When you enable the ACL-based method of filtering RPF failures by entering the mls ip multicast stub
command on the redundant router, the following ACLs automatically download to the PFC and are
applied to the interface you specify:
access-list 100 permit ip A.B.C.0 0.0.0.255 any
access-list 100 permit ip A.B.D.0 0.0.0.255 any
access-list 100 permit ip any 224.0.0.0 0.0.0.255
access-list 100 permit ip any 224.0.1.0 0.0.0.255
access-list 100 deny ip any 224.0.0.0 15.255.255.255
The ACLs filter RPF failures and drop them in hardware so that they are not forwarded to the router.
Use the ACL-based method of filtering RPF failures only in sparse mode stub networks where there are
no downstream routers. For dense mode groups, RPF failure packets have to be seen on the router for
the PIM assert mechanism to function properly. Use CEF-or NetFlow-based rate limiting to rate-limit
RPF failures in dense mode networks and sparse mode transit networks.
For information on configuring ACL-based filtering of RPF failures, see the “Configuring ACL-Based
Filtering of RPF Failures” section on page 18-14.
Rate Limiting of RPF Failure Traffic
Rate limiting of packets that fail the RPF check (non-RPF packets) drops most non-RPF packets in
hardware. According to the multicast protocol specification, the router needs to see the non-RPF packets
for the PIM assert mechanism to work, so all non-RPF packets cannot be dropped in hardware. To
support the PIM assert mechanism, the PFC leaks a percentage of the non-RPF flow packets to the
MSFC.
These sections describe two modes of RPF failure rate limiting:
• NetFlow-Based Rate Limiting of RPF Failures, page 18-7
• CEF-Based Rate Limiting of RPF Failures, page 18-7
Note PFC2 and the DFCs support both rate-limiting modes. CEF-based rate limiting of RPF failures is the
default on systems with PFC2 and for DFCs. NetFlow-based rate limiting of RPF failures is the only rate
limiting mode supported with PFC1.
Network A, B, C.0
Network A, B, D.0
Rest of network
Router A Router B
Mulitcast traffic
non-RPF traffic
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