Dynamic Multicast Configuration Changes; Igmpv2 Back-Down To Igmpv1; Igmpv3 Backward Compatibility - Avaya 8800 Planning And Engineering, Network Design

Multicast network design
239.0.0.0 through 239.127.255.255. A group address range of this size can still easily accommodate
the needs of even the largest private enterprise.

Dynamic multicast configuration changes

Avaya recommends that you do not perform dynamic multicast configuration changes when
multicast streams are flowing in a network. For example, do not change the routing protocol running
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, it may be
necessary for you to disable the multicast routing protocols before performing the change. For
example, consider disabling multicast routing before making interface address changes. In all cases,
these changes result in traffic interruptions because they impact neighbor state machines and
stream state machines.

IGMPv2 back-down to IGMPv1

The DVMRP standard states that when a router operates in Internet Group Management Protocol
version 2 mode (IGMPv2) and another router is discovered on the same subnet in IGMPv1 mode,
the router must back down to IGMPv1 mode. When the Avaya Ethernet Routing Switch8800/ 8600
detects an IGMPv1-only router, it automatically downgrades from IGMPv2 to IGMPv1 mode.
Automatic back-down saves network down time and configuration effort. However, the switch cannot
dynamically change back to IGMPv2 mode because multiple routers now advertise their capabilities
as limited to IGMPv1 only. To return to IGMPv2 mode, the switch must first lose its neighbor
relationship. Subsequently, when the switch reestablishes contact with its neighboring routers, it
operates in IGMPv2 mode.

IGMPv3 backward compatibility

Beginning with Release 5.1, IGMPv3 for PIM-SSM is backward compatible with IGMPv1/v2.
According to RFC 3376, 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, hears an IGMPv1 query or
IGMPv2 general query, it logs a rate-limited warning.
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.
June 2016 Planning and Engineering — Network Design
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