Multimedia Traffic Control with IP Multicast (IGMP)
IGMP General Operation and Features
IGMP General Operation and Features
IGMP Features
Feature
Default
Menu
CLI
view igmp configuration
n/a
—
page 2-7
show igmp status for multicast
n/a
—
Yes
groups used by the selected
VLAN
enabling or disabling IGMP
disabled
—
page 2-9
(Requires VLAN ID Context)
per-port packet control
auto
—
page 2-10
IGMP traffic priority
normal
—
page 2-11
querier enabled
—
page
2-11
fast-leave
disabled
—
page 2-14
In a network where IP multicast traffic is transmitted for various multimedia
applications, you can use the switch to reduce unnecessary bandwidth usage
on a per-port basis by configuring IGMP (Internet Group Management Proto
col controls). In the factory default state (IGMP disabled), the switch simply
floods all IP multicast traffic it receives on a given VLAN through all ports on
that VLAN (except the port on which it received the traffic). This can result
in significant and unnecessary bandwidth usage in networks where IP multi
cast traffic is a factor. Enabling IGMP allows the ports to detect IGMP queries
and report packets and manage IP multicast traffic through the switch.
IGMP is useful in multimedia applications such as LAN TV, desktop confer
encing, and collaborative computing, where there is multipoint communica
tion; that is, communication from one to many hosts, or communication
originating from many hosts and destined for many other hosts. In such
multipoint applications, IGMP will be configured on the hosts, and multicast
traffic will be generated by one or more servers (inside or outside of the local
network). Switches in the network (that support IGMP) can then be config
ured to direct the multicast traffic to only the ports where needed. If multiple
VLANs are configured, you can configure IGMP on a per-VLAN basis.
Enabling IGMP allows detection of IGMP queries and report packets in order
to manage IP multicast traffic through the switch. If no other querier is
detected, the switch will then also function as the querier. (If you need to
disable the querier feature, you can do so through the IGMP configuration
MIB. Refer to “Changing the Querier Configuration Setting” on page 2-11.)
2-3
