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662 PowerConnect B-Series FCX Configuration Guide
53-1002266-01
Configuring IGMP snooping
22
Every group on a physical port keeps its own tracking record. However, it can only track group
membership; it cannot track by (source, group). For example, Client A and Client B belong to group1
but each receives traffic streams from different sources. Client A receives a stream from (source_1,
group1) and Client B receives a stream from (source_2, group1). The device still waits for the
configured leave-wait-time before it stops the traffic because these two clients are in the same
group. If the clients are in different groups, then the waiting period is not applied and traffic is
stopped immediately.
To enable the tracking and fast leave feature for VLAN 20, enter the following commands.
PowerConnect(config)# vlan 20
PowerConnect(config-vlan-20)# multicast tracking
Syntax: [no] multicast tracking
The membership tracking and fast leave features are supported for IGMPv3 only. If any port or any
client is not configured for IGMPv3, then the multicast tracking command is ignored.
Configuring fast leave for IGMPv2
When a device receives an IGMPv2 leave message, it sends out multiple group-specific queries. If
no other client replies within the waiting period, the device stops forwarding traffic. When
fast-leave-v2 is configured, and when the device receives a leave message, it immediately stops
forwarding to that port. The device does not send group specific-queries. You must ensure that no
snooping-enabled ports have multiple clients. When two devices connect together, the querier
must not be configured for fast-leave-v2, because the port might have multiple clients through the
non-querier. The number of queries, and the waiting period (in seconds) can be configured using
the ip multicast leave-wait-time command. The default is 2 seconds.
To configure fast leave for IGMPv2, enter the following commands.
PowerConnect(config)# vlan 20
PowerConnect(config-vlan-20)# multicast fast-leave-v2
Syntax: [no] multicast fast-leave-v2
Enabling fast convergence
In addition to sending periodic general queries, an active device sends general queries when it
detects a new port. However, because the device does not recognize the other device's port up
event, multicast traffic might still require up to the query-interval time to resume after a topology
change. Fast convergence allows the device to listen to topology change events in Layer 2 protocols
such as spanning tree, and then send general queries to shorten the convergence time.
If the Layer 2 protocol cannot detect a topology change, fast convergence may not work in some
cases. For example, if the direct connection between two devices switches from one interface to
another, the rapid spanning tree protocol (802.1w) considers this optimization, rather than a
topology change. In this example, other devices will not receive topology change notifications, and
will be unable to send queries to speed up the convergence. Fast convergence works well with the
regular spanning tree protocol in this case.
To enable fast-convergency, enter the following commands.
PowerConnect(config)# vlan 70
PowerConnect(config-vlan-70)# multicast fast-convergence
Syntax: multicast fast-convergence