Multimedia Traffic Control with IP Multicast (IGMP)

How IGMP Operates

Automatic Fast-Leave IGMP

IGMP Operation Presents a “Delayed Leave” Problem. Where multiple IGMP clients are connected to the same port on an IGMP device (switch or router), if only one IGMP client joins a given multicast group, then later sends a Leave Group message and ceases to belong to that group, the IGMP device retains that IGMP client in its IGMP table and continues forwarding IGMP traffic to the IGMP client until the Querier triggers confirmation that no other group members exist on the same port. This means that the switch continues to transmit unnecessary multicast traffic through the port until the Querier renews the multicast group status.

Fast-Leave IGMP. Depending on the switch model, Fast-Leave is enabled or disabled in the default configuration.

Table 4-2.IGMP: Data-Driven and Non-Data Driven Behavior

Switch Model or

Data-

IGMP Fast-

Default IGMP Behavior

Series

Driven

Leave Setting

 

 

IGMP

 

 

 

Included?

 

 

Switch 8212zl

Yes

Always

Drops unjoined multicast traffic except for

Switch 6400cl

 

Enabled

always-forwarded traffic toward the

Switch 6200yl

 

 

Querier or multicast routers, and out of

 

 

IGMP-forward ports. Selectively forwards

Switch 5400zl

 

 

 

 

joined multicast traffic.

Switch 5300xl

 

 

 

 

 

Switch 4200vl

 

 

 

Switch 3500yl

 

 

 

Switch 3400cl

 

 

 

Switch 2800

 

 

 

Switch 2810

 

 

 

Switch 2510G

 

 

 

Switch 2510-48

 

 

 

Switch 2500

 

 

 

 

 

 

 

Switch 2510-24

No

Disabled in

IGMP Fast-Leave disabled in the default

Switch 2600

 

the Default

configuration. Floods unjoined multicast

Switch 2600-PWR

 

Configuration

traffic to all ports. Selectively forwards

Switch 4100gl

 

 

joined multicast traffic.

Switch 6108

 

 

 

 

 

 

 

On switches that do not support Data-Driven IGMP, unregistered multicast groups are flooded to the VLAN rather than pruned. In this scenario, Fast- Leave IGMP can actually increase the problem of multicast flooding by removing the IGMP group filter before the Querier has recognized the IGMP

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