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15-12
Multimedia Traffic Control with IP Multicast (IGMP)
How IGMP Operates
Multimedia Traffic Control
with IP Multicast (IGMP)
Thus, IGMP identifies members of a multicast group (within a subnet) and
allows IGMP-configured hosts (and routers) to join or leave multicast groups.
IGMP Data. To display data showing active group addresses, reports, que-
ries, querier access port, and active group address data (port, type, and
access), see “Internet Group Management Protocol (IGMP) Status” on page
17-19.
Operation With or Without IP Addressing
You can configure IGMP on VLANs that do not have IP addressing. The benefit
of IGMP without IP addressing is a reduction in the number of IP addresses
you have to use and configure. This can be significant in a network with a large
number of VLANs. The limitation on IGMP without IP addressing is that the
switch cannot become Querier on any VLANs for which it has no IP address—
so the network administrator must ensure that another IGMP device will act
as Querier. It is also advisabale to have an additional IGMP device available
as a backup Querier. See the following table.
Table 15-1.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 multi-
cast router or another switch configured for IGMP oper-
ation. (HP 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 (below) and Forced
Fast-Leave IGMP (page 15-13).
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.