4-17
Multimedia Traffic Control with IP Multicast (IGMP)
How IGMP Operates
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”.
Figure 4-3. 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 switch knows that there is only
one end node on port A3, it removes the client from its IGMP table and halts
multicast traffic (for that group) to port A3. 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 A3. If the switch itself is the Querier, it does not query port
A3 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 A6 in figure 4-3 belong to different VLANs, Fast-Leave does
not operate on port A6.
Using Delayed Group Flush
This feature continues to filter IGMP-Left groups for a specified additional
period of time. The delay in flushing the group filter prevents stale traffic from
being forwarded by the server. Delayed Group Flush is enabled or disabled
for the entire switch.
Routing
Switch
Acting as
Querier
ProCurve Switch with
Automatic Fast-Leave
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 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.
A1 A3
A4
A6
Printer
7D
7B
Syntax:
igmp delayedflush <time period>
Enables the switch to continue to flush IGMP-Left groups
for a specified period of time (0 - 255 seconds). The default
setting is Disabled. To disable, reset the time period to zero.
Syntax: Show igmp delayedflush
Displays the current setting for the switch.
