4-14
Multimedia Traffic Control with IP Multicast (IGMP)
How IGMP Operates
Table 4-1.Comparison of IGMP Operation With and Without IP Addressing
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.
IGMP Function Available With IP Addressing
Configured on the VLAN
Available
Without IP
Addressing?
Operating Differences
Without an IP Address
Forward multicast group traffic to any port on
the VLAN that has received a join request for
that multicast group.
Yes None
Forward join requests (reports) to the Querier. Yes None
Configure individual ports in the VLAN to Auto
(the default)/Blocked, or Forward.
Yes None
Configure IGMP traffic forwarding to normal or
high-priority forwarding.
Yes None
Age-Out IGMP group addresses when the last
IGMP client on a port in the VLAN leaves the
group.
Yes Requires that another IGMP device in the VLAN has an IP
address and can operate as Querier. This can be a
multicast router or another switch configured for IGMP
operation. (ProCurve recommends that the VLAN also
include a device operating as a backup Querier in case
the device operating as the primary Querier fails for any
reason.
Support Fast-Leave IGMP (below) and Forced
Fast-Leave IGMP (page 4-14).
Yes
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.
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