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Enhancements in Release F.02.02
Operation and Enhancements for Multimedia Traffic Control (IGMP)
unnecessary 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 2500 switches automatically uses this Fast-Leave feature.
Automatic Fast-Leave Operation. If a Series 2500 switch port is :
a. Connected to only one end node
b. The end node currently belongs to a multicast group; i.e. is an IGMP client
c. 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 "5B",
but not on the switch port for IGMP clients "7A" and 7B, Server "7C", and printer "7D".
Figure 105. Example of Automatic Fast-Leave IGMP Criteria
When client "3A" running IGMP is ready to leave the multicast group, it transmits a Leave Group
message. Because the Series 2500 switch knows that there is only one end node on port 3, it removes
the client from its IGMP table and halts multicast traffic (for that group) to port 3. If the switch is not
the Querier, it does not wait for the actual Querier to verify that there are no other group members
on port 3. If the switch itself is the Querier, it does not query port 3 for the presence of other group
members.
Note that Fast-Leave operation does not distinguish between end nodes on the same port that belong
to different VLANs. Thus, for example, even if all of the devices on port 7 in figure 105 belong to
different VLANs, Fast-Leave does not operate on port 7.
Routing
Switch
Acting as
Querier
Series 2500 Switch
Server
7C
Switch 7X
3A
5A
7A
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 2500 switch
detects multiple end
nodes on that port.
Fast-Leave IGMP does
not activate on this port.
Fast-Leave IGMP
activates on these
two ports.
1
3
5
7
Printer
7D
7B