HP ProCurve 5300xl Series Management Manual page 118

Multimedia Traffic Control with IP Multicast (IGMP)
How IGMP Operates
Fast-Leave IGMP
automatically operates on
the ports connected to
IGMP clients 3A and 5A,
but does not operate on
the port connected to
Switch 7X because the
Series 5300XL switch
detects multiple end
nodes on that port.
Figure 4-3. Example of Automatic Fast-Leave IGMP Criteria
4-14
group members exist on the same port. This delayed leave operation means
that the switch continues to transmit unnecessary multicast traffic through
the port until the Querier renews multicast group status.
Fast-Leave IGMP Reduces Leave Delays. Fast-Leave IGMP operates on a
port if an IGMP client connects to the port and there are no other end nodes
detected on that port. In this case, when the client leaves a multicast group,
Fast-Leave IGMP automatically accelerates the blocking of further, unneces­
sary multicast traffic from that group to the former IGMP client. This improves
performance by reducing the amount of multicast traffic going through the
port to the IGMP client after the client leaves a multicast group. IGMP in the
Series 5300XL switches automatically uses this Fast-Leave feature.
Automatic Fast-Leave Operation. If a switch port has the following char­
acteristics, then the Fast-Leave operation will apply:
1. Connected to only one end node
2. The end node currently belongs to a multicast group; i.e. is an IGMP client
3. The end node subsequently leaves the multicast group
Then the switch does not need to wait for the Querier status update interval,
but instead immediately removes the IGMP client from its IGMP table and
ceases transmitting IGMP traffic to the client. (If the switch detects multiple
end nodes on the port, automatic Fast-Leave does not activate—regardless of
whether one or more of these end nodes are IGMP clients.)
In the next figure, automatic Fast-Leave operates on the switch ports for IGMP
clients "3A" and "5A", but not on the switch port for IGMP clients "7A" and 7B,
Server "7C", and printer "7D".
Fast-Leave IGMP
activates on these
two ports.
Routing
Switch
Acting as
Querier
When client "3A" running IGMP is ready to leave the multicast group, it
transmits a Leave Group message. Because the switch knows that there is only
one end node on port A3, it removes the client from its IGMP table and halts
5A
3A
A6
A1 A3 A4
Series 5300XL switch
Server
7B
7A
7C
Switch 7X
Printer
Fast-Leave IGMP does
not activate on this port.
7D