38-5
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 38 Configuring IP Multicast
About IP Multicast
Figure 38-2 Logical View of Layer 2 and Layer 3 Forwarding in Hardware
This section contains the following subsections:
• Restrictions on IP Multicast, page 38-5
• CEF, MFIB, and Layer 2 Forwarding, page 38-6
• IP Multicast Tables, page 38-7
• Hardware and Software Forwarding, page 38-9
• Non-Reverse Path Forwarding Traffic, page 38-10
• Multicast Fast Drop, page 38-11
• Multicast Forwarding Information Base, page 38-12
• S/M, 224/4, page 38-13
• Multicast HA, page 38-13
Restrictions on IP Multicast
Restrictions on IP Multicast include the following:
• Packets that have a multicast destination IP address and unicast MAC address are dropped.
• Starting with Release IOS XE 3.3.0SG and IOS 15.1(1)SG, the seven RP restriction was removed.
• IPv4 Bidirectional (Bidir) PIM is supported on the Catalyst 4500 series switch. IPv6 Bidir PIM is
not.
• For some multicast groups, when more than 8K mroutes are installed in a system, the network may
experience higher traffic losses upon switchover of the HA system. This is due to flushing the old
multicast forwarding entries before the new entries are updated. As the number of routes increase,
more time is required for the entries to be updated in the MFIB. To reduce the traffic loss in this
scenario, you should increase the multicast route-flush timer (using the ip multicast redundancy
routeflush maxtime command) to a value exceeding the default (30 seconds).
Integrated Switching Engine (ASIC)
L3 physical
interface
Logical Router
L3 logical
interfaces
L2 switchports
68402
VLAN1
Gig 1/1
VLAN2
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