Design Reference

to flow from sources to receivers. A multicast router normally provides the IGMP querier function.
You can use the IGMP Layer 2 querier to provide a querier on a Layer 2 network without a multicast
router.
The Layer 2 querier function originates queries for multicast receivers, and processes the responses
accordingly. On the connected Layer 2 VLANs, IGMP snoop continues to provide services as
normal. IGMP snoop responds to queries and identifies receivers for the multicast traffic.
You must enable Layer 2 querier and configure an IP address for the querier before it can originate
IGMP query messages. If a multicast router exists on the network, VSP 4000 automatically disables
the Layer 2 querier.
In a Layer 2 multicast network, enable Layer 2 querier on only one of the switches in the VLAN. A
Layer 2 multicast domain supports only one Layer 2 querier. No querier election exists.
For more information about how to configure IGMP Layer 2 querier, see Configuring IP Multicast
Routing Protocols on Avaya Virtual Services Platform 4000 Series , NN46251–504.
TTL in IP multicast packets
Avaya Virtual Services Platform 4000 Series treats multicast data packets with a time-to-live (TTL)
of 1 as expired packets and sends them to the CPU before dropping them. To avoid this issue,
ensure that the originating application uses a hop count large enough to enable the multicast stream
to traverse the network and reach all destinations without reaching a TTL of 1. Avaya recommends
that you use a TTL value of 33 or 34 to minimize the effect of looping in an unstable network.
Multicast MAC filtering
Certain network applications, such as the Microsoft Network Load Balancing solution, require
multiple hosts to share a multicast MAC address. Instead of flooding all ports in the VLAN with this
multicast traffic, you can use Multicast MAC filtering to forward traffic to a configured subset of the
ports in the VLAN. This multicast MAC address is not an IP multicast MAC address.
At a minimum, map the multicast MAC address to a set of ports within the VLAN. In addition, if traffic
is routed on the local VSP 4000, you must configure an Address Resolution Protocol (ARP) entry to
map the shared unicast IP address to the shared multicast MAC address. You must configure an
ARP entry because the hosts can also share a virtual IP address, and packets addressed to the
virtual IP address need to reach each host.
Avaya recommends that you limit the number of such configured multicast MAC addresses to a
maximum of 100. This number is related to the maximum number of possible VLANs you can
configure, because for every multicast MAC filter that you configure the maximum number of
configurable VLANs reduces by one. Similarly, configuring large numbers of VLANs reduces the
maximum number of configurable multicast MAC filters downward from 100.
IP multicast network design
112 Network Design Reference for Avaya VSP 4000 Series January 2015
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