Layer 2 Multicast Features; Igmp Snoop And Proxy - Avaya 8800 Planning And Engineering

Multicast network design
the hosts on that subnet. The split-subnet problem applies to any type of traffic. However, it
has a larger impact on a PIM-SM network.
To avoid the split-subnet problem in PIM networks, ensure that the Rendezvous Point (RP)
router is not located in a subnet that can become a split subnet. Also, avoid having receivers
on this subnet. Because the RP is an entity that must be reached by all PIM-enabled switches
with receivers in a network, placing the RP on a split-subnet can impact the whole multicast
traffic flow. Traffic can be affected even for receivers and senders that are not part of the split-
subnet.

Layer 2 multicast features

On Layer 2 VLANs, the Avaya Ethernet Routing Switch 8800/8600 provides the following
features to support multicast traffic.
•

IGMP snoop and proxy

• Multicast VLAN Registration (MVR)
• IGMP Layer 2 querier
IGMP snoop and proxy
On a Layer 2 VLAN, if at least one host on the VLAN specifies that it is a member of a multicast
group, by default, the Avaya Ethernet Routing Switch 8800/8600 forwards to that VLAN all
datagrams bearing the multicast address of that group. All ports on the VLAN receive the traffic
for that group.
With IGMP snoop enabled on a VLAN, the Avaya Ethernet Routing Switch 8800/8600 forwards
the multicast group data to only those ports that are members of the multicast group.
The switch identifies multicast group members by listening to IGMP packets (IGMP reports,
leaves, and queries) from each port. Using the information gathered from the reports, the switch
builds a list of group members. After the group members are identified, the switch blocks the
IP Multicast stream from exiting any port that does not connect to a group member, conserving
bandwidth.
With IGMP snoop enabled, the switch can receive multiple reports for the same multicast
group. Rather than forward each report upstream, the Ethernet Routing Switch 8800/8600 can
consolidate these multiple reports using the IGMP proxy feature. With IGMP proxy enabled, if
the switch receives multiple reports for the same multicast group, it does not transmit each
report to the upstream multicast router. Instead, the switch forwards the first report to the
querier and suppresses the rest. If new information emerges, for example if the switch adds
another multicast group or receives a query since the last report is transmitted upstream, then
the switch forwards a new report to the multicast router ports.
162 Planning and Engineering — Network Design
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November 2010