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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 28 Configuring IPv4 Multicast Layer 3 Switching
IPv4 Multicast Layer 3 Switching Configuration Guidelines and Restrictions
Internet Group Management Protocol (IGMP) snooping is enabled by default on all VLAN interfaces. If
you disable IGMP snooping on an interface, multicast Layer 3 flows are still switched by the hardware.
Bridging of the flow on an interface with IGMP snooping disabled causes flooding to all forwarding
interfaces of the VLAN. For details on configuring IGMP snooping, see Chapter 30, “Configuring IGMP
Snooping for IPv4 Multicast Traffic.”
IPv4 Multicast Layer 3 Switching Configuration Guidelines and
Restrictions
These sections describe IP Multicast Layer 3 switching configuration restrictions:
• Restrictions, page 28-8
• Unsupported Features, page 28-9
Restrictions
IP multicast Layer 3 switching is not provided for an IP multicast flow in the following situations:
• For IP multicast groups that fall into the range 224.0.0.* (where * is in the range 0 to 255), which
is used by routing protocols. Layer 3 switching is supported for groups 224.0.2.* to 239.*.*.*.
Note Groups in the 224.0.0.* range are reserved for routing control packets and must be flooded
to all forwarding ports of the VLAN. These addresses map to the multicast MAC address
range 01-00-5E-00-00-xx, where xx is in the range 0–0xFF.
• For PIM auto-RP multicast groups (IP multicast group addresses 224.0.1.39 and 224.0.1.40).
• For packets with IP options. However, packets in the flow that do not specify IP options are hardware
switched.
• For source traffic received on tunnel interfaces (such as MBONE traffic).
• If a (S,G) entry for sparse mode does not have the SPT-bit, RPT-bit, or Pruned flag set.
• A (*,G) entry is not hardware switched if at least one (S,G) entry has an RPF different from the (*,G)
entry’s RPF and the (S,G) is not hardware switched.
Table 28-1 Default IP Multicast Layer 3 Switching Configuration
Feature Default Value
ACL for stub networks Disabled on all interfaces
Installing of directly connected subnet entries Enabled globally
Multicast routing Disabled globally
PIM routing Disabled on all interfaces
IP multicast Layer 3 switching Enabled when multicast routing is enabled and PIM
is enabled on the interface
Shortcut consistency checking Enabled
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