Table 2: Comparison of IGMP operation with and without IP addressing
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. (Hewlett Packard Enterprise
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 and Forced
Fast-Leave IGMP (below.)
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.
Automatic fast-leave IGMP
Depending on the switch model, fast-leave is enabled or disabled in the default configuration.
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 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 fast-leave feature is disabled by default on
all switches that do not support data-driven IGMP (see the table above.) The feature can be enabled on these
switches via an SNMP set of this object:
hpSwitchIgmpPortForceLeaveState.
vid
.
port number
However, Hewlett Packard Enterprise does not recommend this, because it 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
information on this topic, see
32
Aruba 3810 / 5400R Multicast and Routing Guide for ArubaOS-
Switch 16.08