Specifications

Configuring IP Multicast Multilayer Switching
Restrictions
2
• IP multicast routing and PIM must be enabled on the router. The minimal steps to configure them
are described in the “Configuring and Monitoring IP Multicast MLS” section later in this document.
For detailed information on configuring IP multicast routing and PIM, refer to the Cisco IOS IP
Routing Configuration Guide.
Restrictions
You must also configure the Catalyst 5000 series switch in order for IP multicast MLS to function on the
router.
The restrictions in the following sections apply to IP multicast MLS on the router:
• Router Configuration Restrictions
• External Router Guidelines
• Access List Restrictions and Guidelines
Router Configuration Restrictions
IP multicast MLS does not work on internal or external routers in the following situations:
• If IP multicast MLS is disabled on the RPF interface for the flow (using the no mls rp ip multicast
interface configuration command).
• For IP multicast groups that fall into these ranges (where * is in the range from 0 to 255):
– 224.0.0.* through 239.0.0.*
– 224.128.0.* through 239.128.0.*
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 from 0 to 0xFF.
• For PIM auto-RP multicast groups (IP multicast group addresses 224.0.1.39 and 224.0.1.40).
• For flows that are forwarded on the multicast shared tree (that is, {*, G, *} forwarding) when the
interface or group is running PIM sparse mode.
• If the shortest path tree (SPT) bit for the flow is cleared when running PIM sparse mode for the
interface or group.
• When an input rate limit is applied on an RPF interface.
• For any RPF interface with access lists applied (for detailed information, see the “Access List
Restrictions and Guidelines” section later in this document).
• For any RPF interface with multicast boundary configured.
• For packets that require fragmentation and packets with IP options. However, packets in the flow
that are not fragmented or that do not specify IP options are multilayer switched.
• On external routers, for source traffic received at the router on non-ISL or non-802.1Q interfaces.
• For source traffic received on tunnel interfaces (such as MBONE traffic).
• For any RPF interface with multicast tag switching enabled.