Cisco WS-C6506 Software Manual page 327

Chapter 13 Configuring CEF for PFC2 and PFC3A
Partially and Completely Switched Multicast Flows
Some flows might be partially Layer 3 switched instead of completely Layer 3 switched in these
situations:
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CEF for PFC2/PFC3A provides Layer 3 switching when the extended access list deny condition on the
Note
RPF interface specifies something other than the Layer 3 source, Layer 3 destination, or IP protocol (an
example is the Layer 4 port numbers).
For partially switched flows, all multicast traffic belonging to the flow reaches MSFC2/MSFC3 and is
software switched for any interface that is not Layer 3 switched.
All (*,G) flows are always partially Layer 3 switched.
Note
PFC2/PFC3A prevents multicast traffic in flows that are completely Layer 3 switched from reaching
MSFC2/MSFC3, reducing the load on MSFC2/MSFC3. The show ip mroute and show mls ip multicast
commands identify completely Layer 3-switched flows with the text string "RPF-MFD." Multicast Fast
Drop (MFD) indicates that from the perspective of MSFC2/MSFC3, the multicast packet is dropped,
because it is switched by the PFC2/PFC3A.
For all completely Layer 3-switched flows, PFC2/PFC3A periodically sends multicast packet and byte
count statistics to MSFC2/MSFC3, because MSFC2/MSFC3 cannot record multicast statistics for
completely switched flows, which it never sees. MSFC2/MSFC3 uses the statistics to update the
corresponding multicast routing table entries and reset the appropriate expiration timers.
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MSFC2/MSFC3 is configured as a member of the IP multicast group (using the ip igmp join-group
command) on the RPF interface of the multicast source.
MSFC2/MSFC3 is the first-hop router to the source in PIM sparse mode (in this case,
MSFC2/MSFC3 must send PIM-register messages to the rendezvous point).
The multicast TTL threshold is configured on an egress interface for the flow.
The multicast helper is configured on the RPF interface for the flow, and multicast to broadcast
translation is required.
Multicast tag switching is configured on an egress interface.
Network Address Translation (NAT) is configured on an interface, and source address translation is
required for the outgoing interface.
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
Understanding How Layer 3 Switching Works
13-9