Multimedia Traffic Control with IP Multicast (IGMP)

How IGMP Operates

Table 4-1.Comparison of IGMP Operation With and Without IP Addressing

IGMP Function Available With IP Addressing

Available

Operating Differences

Configured on the VLAN

Without IP

Without an IP Address

 

Addressing?

 

 

 

 

Forward multicast group traffic to any port on

Yes

None

the VLAN that has received a join request for

 

 

that multicast group.

 

 

 

 

 

Forward join requests (reports) to the Querier.

Yes

None

 

 

 

Configure individual ports in the VLAN to Auto

Yes

None

(the default)/Blocked, or Forward.

 

 

 

 

 

Configure IGMP traffic forwarding to normal or

Yes

None

high-priority forwarding.

 

 

 

 

 

 

 

 

Age-Out IGMP group addresses when the last

Yes

Requires that another IGMP device in the VLAN has an IP

IGMP client on a port in the VLAN leaves the

 

address and can operate as Querier. This can be a

group.

 

multicast router or another switch configured for IGMP

 

 

operation. (ProCurve recommends that the VLAN also

Support Fast-Leave IGMP (below) and Forced

Yes

include a device operating as a backup Querier in case

Fast-Leave IGMP (page 4-14).

 

the device operating as the primary Querier fails for any

 

 

reason.

 

 

 

Support automatic Querier election.

No

Querier operation not available.

 

 

 

Operate as the Querier.

No

Querier operation not available.

 

 

 

Available as a backup Querier.

No

Querier operation not available.

 

 

 

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.

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