HP ProCurve Series 2810 Management And Configuration Manual page 91

Table 4-2.IGMP: Data-Driven and Non-Data Driven Behavior
Switch Model or Data-
Series Driven
IGMP
Included?
Switch 5300 Yes
Switch 2800
Switch 2810
Switch 2500
Switch 2600 No
Switch 2600-PWR
Switch 4100
Switch 6108
On switches that do not support Data-Driven IGMP, unregistered multicast
groups are flooded to the VLAN rather than pruned. In this scenario, Fast-
Leave IGMP can actually increase the problem of multicast flooding by
removing the IGMP group filter before the Querier has recognized the IGMP
Leave. The Querier will continue to transmit the multicast group during this
short time, and because the group is no longer registered the switch will then
flood the multicast group to all ports.
On ProCurve switches that do support Data-Driven IGMP ("Smart" IGMP),
when unregistered multicasts are received the switch automatically filters
(drops) them. Thus, the sooner the IGMP Leave is processed, the sooner this
multicast traffic stops flowing.
Because of the multicast flooding problem mentioned above, the IGMP
FastLeave feature is disabled by default on all ProCurve switches that do not
support Data-Driven IGMP. (See table 4-2, above.) The feature can be enabled
on these switches via an SNMP set of this object:
hpSwitchIgmpPortForceLeaveState.< vid >.< port number>
However, this is not recommended as this will increase the amount of
multicast flooding during the period between the client's IGMP Leave and the
Querier's processing of that Leave. For more on this topic, refer to "Forced
Fast-Leave IGMP" on page 4-17.
ProCurve recommends that the following settings be used.
■ Use Delayed Group Flush on the Series 2600 switches whenever Fast
Leave or Forced Fast Leave are set on a port (see page 4-17).
■ Forced fast leave can be used when there are multiple devices
attached to a port.
Multimedia Traffic Control with IP Multicast (IGMP)
IGMP Fast- Default IGMP Behavior
Leave Setting
Always Drops unjoined multicast traffic except for
Enabled always-forwarded traffic toward the Querier
or multicast routers, and out of IGMP-forward
ports. Selectively forwards joined multicast
traffic.
Disabled in IGMP Fast-Leave disabled in the default
the Default configuration. Floods unjoined multicast
Configuration traffic to all ports. Selectively forwards joined
multicast traffic.
How IGMP Operates
4-15