Specifications

Overview
ExtremeWare XOS 11.0 Concepts Guide 305
IGMP Overview
IGMP is a protocol used by an IP host to register its IP multicast group membership with a router.
Periodically, the router queries the multicast group to see if the group is still in use. If the group is still
active, a single IP host responds to the query, and group registration is maintained.
IGMP is enabled by default on the switch. However, the switch can be configured to disable the
generation of periodic IGMP query packets. IGMP should be enabled when the switch is configured to
perform IP unicast or IP multicast routing.
IGMP Snooping
IGMP snooping is a Layer 2 function of the switch; it does not require multicast routing to be enabled.
In IGMP snooping, the Layer 2 switch keeps track of IGMP reports and only forwards multicast traffic
to that part of the local network that requires it. IGMP snooping optimizes the use of network
bandwidth and prevents multicast traffic from being flooded to parts of the local network that do not
need it.
IGMP snooping is enabled by default on the switch. If IGMP snooping is disabled, all IGMP and IP
multicast traffic floods within a given VLAN. IGMP snooping expects at least one device on every
VLAN to periodically generate IGMP query messages. The static IGMP snooping entries do not require
periodic query, but these entries do require a query in order to retrieve them after the
clear igmp
snooping
command.
When a port sends an IGMP leave message, the switch removes the IGMP snooping entry after 1000
milliseconds (the leave time is configurable, ranging from 0 to 10000 ms). The switch sends a query to
determine which ports want to remain in the multicast group. If other members of the VLAN want to
remain in the multicast group, the router ignores the leave message, but the port that requests removal
is removed from the IGMP snooping table.
If the last port within a VLAN sends an IGMP leave message and the router does not receive any
responses to the query, then the router immediately removes the VLAN from the multicast group.
Static IGMP
To receive multicast traffic, a host must explicitly join a multicast group by sending an IGMP report;
then, the traffic is forwarded to that host. In some situations, you would like multicast traffic to be
forwarded to a port where a multicast-enabled host is not available (for example, when you test
multicast configurations). Static IGMP emulates a host or router attached to a switch port, so that
multicast traffic is forwarded to that port. You can emulate a host to forward a particular multicast
group to a port; and you may emulate a router to forward all multicast groups to a port. Use the
following command to emulate a host on a port:
configure igmp snooping {vlan} <vlanname> ports <portlist> add static group <ip
address>
To emulate a multicast router on a port, use the following command:
configure igmp snooping {vlan} <vlanname> ports <portlist> add static router
To remove these entries, use the corresponding command:
configure igmp snooping {vlan} <vlanname> ports <portlist> delete static
group [<ip_address> | all]
configure igmp snooping vlan <vlanname> ports <portlist> delete static router