Multimedia Traffic Control with IP Multicast (IGMP)

How IGMP Operates

4-2.Switches Supported for IGMP Features

Switch Model

Data-

IGMP Fast-

Default IGMP Behavior

or Series

Driven

Leave Setting

 

 

IGMP

 

 

 

Included?

 

 

Switch 8212zl

Yes

Always

Drops unjoined mulitcast traffic except for

Switch 6400cl

 

Enabled

always-fowarded traffic toward the Querier or

Switch 6200yl

 

 

multicast routers, and out of IGMP-forward

 

 

ports. Selectively forwards joined multicast

Switch 5400zl

 

 

 

 

traffic.

Switch 5300xl

 

 

 

 

 

Switch 4200vl

 

 

 

Switch 3500yl

 

 

 

Switch 3400cl

 

 

 

Switch 2610

 

 

 

Switch 2610­

 

 

 

PWR

 

 

 

Switch 2500

 

 

 

 

 

 

 

Switch 2600

No

Disabled in

IGMP Fast-Leave disabled in the default

Switch 2600­

 

the Default

configuration. Floods unjoined multicast traffic

PWR

 

Configuration

to all ports. Selectively forwards joined

Switch 4100gl

 

 

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 Leave. The Querier will continue to transmit the multicast group during this short time, and because the group is no longer registered the switch will then flood the multicast group to all ports.

The switches covered in this guide support Data-Driven IGMP (“Smart” IGMP), which is enabled by default. Data-Driven IGMP prunes off any unregistered IGMP streams detected on the switch. Thus, the sooner the IGMP Leave is processed, the sooner this multicast traffic stops flowing.

Because of the multicast flooding problem mentioned above, the IGMP FastLeave feature is disabled by default on all ProCurve switches that do not support Data-Driven IGMP. (See table 4-2,above.) The feature can be enabled on these switches via an SNMP set of this object:

hpSwitchIgmpPortForceLeaveState.< vid >.< port number >

However, this is not recommended as this will increase the amount of multicast flooding during the period between the client's IGMP Leave and the

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