Design Reference

Dynamic multicast configuration changes
Avaya recommends that you not perform dynamic multicast configuration changes when multicast
streams flow in a network. For example, do not change the routing protocol that runs on an
interface, or the IP address, or the subnet mask for an interface until multicast traffic ceases.
For such changes, Avaya recommends that you temporarily stop all multicast traffic. If the changes
are necessary and you have no control over the applications that send multicast data, you can
disable the multicast routing protocols before you perform the change. For example, consider
disabling multicast routing before making interface address changes. In all cases, these changes
result in traffic interruptions because they affect neighbor-state machines and stream-state
machines.
In addition, Avaya recommends that when removing port members of an MLT group you first disable
the ports. Changing the group set without first shutting the ports down can result in high-CPU
utilization and processing in a scaled multicast environment due to the necessary hardware
reprogramming on the multicast records.
IGMPv3 backward compatibility
IGMPv3 for PIM is backward compatible with IGMPv1/v2. According to RFC3376, the multicast
router with IGMPv3 can use one of two methods to handle older query messages:
• If an older version of IGMP is present on the router, the querier must use the lowest version of
IGMP present on the network.
• If a router that is not explicitly configured to use IGMPv1 or IGMPv2, detects an IGMPv1 query
or IGMPv2 general query, it logs a rate-limited warning.
You can configure the IGMP version of an interface to version 3 regardless of the PIM or snooping
mode.
You can configure whether the switch downgrades the version of IGMP to handle older query
messages. If the switch downgrades, the host with IGMPv3 only capability does not work. If you do
not configure the switch to downgrade the version of IGMP, the switch logs a warning.
Note:
If you enable the explicit host tracking option on an IGMPv3 interface, you cannot downgrade to
IGMPv1 or IGMPv2. You must disable explicit host tracking to downgrade the IGMP version.
IGMP Layer 2 Querier
In a multicast network, if you only need to use Layer 2 switching for the multicast traffic, you do not
need multicast routing. However, you must have an IGMP querier on the network for multicast traffic
Dynamic multicast configuration changes
December 2014 Network Design Reference for Avaya VSP 4000 Series 109
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