Multimedia Traffic Control with IP Multicast (IGMP)
How IGMP Operates
TableIGMP Function Available With IP Addressing | Available | Operating Differences | |
Configured on the VLAN | Without IP | Without an IP Address | |
| Addressing? |
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Forward multicast group traffic to any port on | Yes | None | |
the VLAN that has received a join request for |
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that multicast group. |
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Forward join requests (reports) to the Querier. | Yes | None | |
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Configure individual ports in the VLAN to Auto | Yes | None | |
(the default)/Blocked, or Forward. |
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Configure IGMP traffic forwarding to normal or | Yes | None | |
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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 | |
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| operation. (ProCurve recommends that the VLAN also | |
Support | Yes | ||
include a device operating as a backup Querier in case | |||
| the device operating as the primary Querier fails for any | ||
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| reason. | |
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Support automatic Querier election. | No | Querier operation not available. | |
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Operate as the Querier. | No | Querier operation not available. | |
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Available as a backup Querier. | No | Querier operation not available. | |
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Automatic
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.