Cisco WS-C6506 Software Manual page 361

Chapter 14 Configuring MLS
The PFC uses the Layer 2 multicast forwarding table to identify the ports to which Layer 2 multicast
Note
traffic should be forwarded (if any). The multicast forwarding table entries are populated by whichever
multicast constraint feature is enabled on the switch (IGMP snooping or Generic Attribute Registration
Protocol [GARP] Multicast Registration Protocol [GMRP]). These entries map the destination multicast
MAC address to the outgoing switch ports for a given VLAN.
Understanding the MLS Cache
These sections describe the MLS cache:
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MLS Cache
The PFC maintains a Layer 3 switching table called the MLS cache for the Layer 3-switched flows. The
cache also includes the entries for the traffic statistics that are updated simultaneously with the switching
of packets. After the PFC creates an MLS cache entry, the packets that are identified as belonging to an
existing flow can be Layer 3 switched based on the cached information. The MLS cache maintains flow
information for all the active flows.
Unicast Traffic
For unicast traffic, the PFC creates an MLS cache entry for the initial routed packet of each unicast flow.
Upon receipt of a routed packet that does not match any unicast flow currently in the MLS cache, the
PFC creates a new MLS entry.
Multicast Traffic
For multicast traffic, the PFC populates the MLS cache using information that is learned from the MSFC.
Whenever the MSFC receives traffic for a new multicast flow, it updates its multicast routing table and
forwards the new information to the PFC. In addition, if an entry in the multicast routing table ages out,
the MSFC deletes the entry and forwards the updated information to the PFC.
For each multicast flow cache entry, the PFC maintains a list of outgoing interfaces for the destination
IP multicast group. The PFC uses this list to identify the VLANs on which traffic to a given multicast
flow should be replicated.
These Cisco IOS commands affect the multicast MLS cache entries on the switch:
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OL-8978-04
MLS Cache, page 14-5
Unicast Traffic, page 14-5
Multicast Traffic, page 14-5
MLS Cache Aging, page 14-6
MLS Cache Size, page 14-6
Using the clear ip mroute command to clear the multicast routing table on the MSFC clears all
multicast MLS cache entries on the PFC.
Using the no ip multicast-routing command to disable IP multicast routing on the MSFC purges
all multicast MLS cache entries on the PFC.
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
Understanding How Layer 3 Switching Works
14-5