Brocade Multi-Service IronWare Multicast Configuration Guide (Supporting R05.6.00) - Manual (Page 143)

Multi-Service IronWare Multicast Configuration Guide 131
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IP multicast traffic reduction
1
In the example shown in Figure 18 , when IP multicast traffic reduction (IGMP snooping) is enabled
on the VPLS network, PE 1 will be selected as the active port (querier) because it has the lowest
router ID amongst the PEs in the VPLS instance. PE 1 will actively send out IGMP queries to solicit
information from IP multicast groups within the VPLS instance. PE 2 and PE 3 will not send out
queries as they are in passive mode, but will respond to the query from PE 1, with the respective
report information received from their hosts.
In a snooping configuration within a VPLS instance, multicast traffic is always flooded to the device
that is in active IGMP mode (the router port). If the IP multicast domain includes an IP multicast
router, that router will be the querier. In this case, the querier is also known as the router port. If
there is no IP multicast router in the domain, one of the devices in the network can be manually
configured for active IGMP mode. Otherwise, the device with the lowest router ID will be elected as
the querier. In the example in
Figure 18 , PE 1 is the elected querier.
In a VPLS scenario, reports are always forwarded to all VPLS peers whether or not the peer is the
querier. In the above example, PE 1 is elected the querier, but if PE 2 is connected to a receiver, it
forwards the reports received from the receiver to both VPLS peers PE 3 and PE 1. Therefore, any
traffic for the host connected to PE 2 received from PE 3 are sent by PE 3 to both the router port PE
1 as well as the receiver PE 2.
PE 1 drops the traffic received from PE 3 because it is aware of the presence of a receiver attached
to the router PE 2. Traffic sent from PE 3 will only be received by the host connected to PE 2.
If there is no receiver present in the setup, then traffic from PE 3 will only be flooded to its local
endpoints and the router port PE 1. Router PE 1 sends the traffic out of its endpoints.
In case of PIM SM snooping, traffic received for unknown groups is always dropped. There is no
router port concept in case of PIM SM snooping.
Multicast Traffic Forwarding
Brocade MLX series and Brocade NetIron XMR devices use the IP multicast group address for data
forwarding when supporting multicast traffic reduction over VPLS.
On Brocade NetIron CES and Brocade NetIron CER devices, data forwarding uses the destination
multicast MAC address. The IP multicast group address is mapped to its destination MAC address.
The MAC address is programmed as the VPLS MAC entry for the IP multicast group.
Implementing data forwarding, using the destination multicast MAC address, has the following
limitations on Brocade NetIron CES and Brocade NetIron CER devices:
• Data forwarding based on the source IP address is not supported.
• All packets with destination multicast MAC address are forwarded, including IP unicast
packets, IP multicast packets that did not follow the standard mapping, and non-IP packets.
• When a number of IP group addresses map to the same destination multicast MAC address,
the output ports are the superset of all the output ports of the IP group addresses mapped to
the destination multicast MAC address. As a result, some hosts receive unwanted traffic. For
example, IP groups G1 and G2 map to the same destination multicast MAC address. If G1
contains port 1 and port 2 and G2 contains port 2 and port 3, traffic sent to G1 and G2 will be
forwarded to ports 1, 2, and 3. Hosts that are connected to port 1 and port 3 will receive
unwanted traffic.
Configuring the IGMP mode per VLAN or VPLS instance
In the following example, multicast traffic reduction is applied using IGMP snooping to VLAN 2.