Specifications

Configuring IP Multicast Multilayer Switching
IP Multicast MLS Configuration Examples
7
Operation Before IP Multicast MLS Example
Without IP multicast MLS, when the G1 source (on VLAN 10) sends traffic destined for IP multicast
group G1, the switch forwards the traffic (based on the Layer 2 multicast forwarding table entry
generated by the IGMP snooping, CGMP, or GMRP multicast service) to Host A on VLAN 10 and to
the router subinterface in VLAN 10.
The router receives the multicast traffic on its incoming subinterface for VLAN 10, checks the multicast
routing table, and replicates the traffic to the outgoing subinterfaces for VLANs 20 and 30. The switch
receives the traffic on VLANs 20 and 30 and forwards the traffic received on these VLANs to the
appropriate switch ports, again based on the contents of the Layer 2 multicast forwarding table.
Operation After IP Multicast MLS Example
After IP multicast MLS is implemented, when the G1 source sends traffic destined for multicast group
G1, the MMLS-SE checks its Layer 3 multicast MLS cache and recognizes that the traffic belongs to a
multicast MLS flow. The MMLS-SE forwards the traffic to Host A on VLAN 10 based on the multicast
forwarding table, but does not forward the traffic to the router subinterface in VLAN 10 (assuming a
completely switched flow).
For each multicast MLS cache entry, the switch maintains a list of outgoing interfaces for the destination
IP multicast group. The switch replicates the traffic on the appropriate outgoing interfaces (VLANs 20
and 30) and then forwards the traffic on each VLAN to the destination hosts (using the Layer 2 multicast
forwarding table). The switch performs a packet rewrite for the replicated traffic so that the packets
appear to have been routed by the appropriate router subinterface.
If not all the router subinterfaces are eligible to participate in IP multicast MLS, the switch must forward
the multicast traffic to the router subinterface in the source VLAN (in this case, VLAN 10). In this
situation, on those subinterfaces that are ineligible, the router performs multicast forwarding and
replication in software, in the usual manner. On those subinterfaces that are eligible, the switch performs
multilayer switching.
Note On the MMLS-RP, the IP multicast MLS management interface is user-configured to the VLAN 30
subinterface. If this interface goes down, the system will revert to the default management interface (in
this case, the VLAN 10 subinterface).
Router Configuration
The following is an example configuration of IP multicast MLS on the router:
ip multicast-routing
interface fastethernet2/0.10
encapsulation isl 10
ip address 10.1.10.1 255.255.255.0
ip pim dense-mode
interface fastethernet2/0.20
encapsulation isl 20
ip address 10.1.20.1 255.255.255.0
ip pim dense-mode
interface fastethernet2/0.30
encapsulation isl 30
ip address 10.1.30.1 255.255.255.0
ip pim dense-mode
mls rp ip multicast management-interface