Configuring the ECN330-switch
364 1553-KDU 137 365 Uen D 2006-06-16
6.16.3 Layer 3 IGMP (Query used with Multicast Routing)
IGMP Snooping – IGMP Snooping is a Layer 2 function (page 355) that can be
used to provide multicast filtering when no other switches in the network support
multicast routing. (Note that IGMP Snooping can only be globally enabled.)
IGMP Query – Multicast query is used to poll each known multicast group for
active members, and dynamically configure the ECN330 ports which need to
forward multicast traffic. Although the implementation differs slightly, IGMP
Query is used in conjunction with both Layer 2 IGMP Snooping and multicast
routing. Note that when using IGMP Snooping, multicast query is automatically
enabled. (See 6.16.2.1 "Configuring IGMP Snooping and Query Parameters"
355.)
Layer 3 IGMP – This protocol includes a form of multicast query specifically
designed to work with multicast routing. A router periodically asks its hosts if
they want to receive multicast traffic. It then propagates service requests on to
any upstream multicast router to ensure that it will continue to receive the
multicast service. Layer 3 IGMP can be enabled for individual VLAN interfaces
(page 362). (Note that Layer 2 snooping and query is disabled if Layer 3 IGMP
is enabled.)
6.16.3.1 Configuring IGMP Interface Parameters
The ECN330-switch uses IGMP (Internet Group Management Protocol) to
query for any attached hosts that want to receive a specific multicast service.
The hosts may respond with several types of IP multicast messages. Hosts
respond to queries with report messages that indicate which groups they want
to join or the groups to which they already belong. If a router does not receive a
report message within a specified period of time, it will prune that interface from
the multicast tree. A host can also submit a join message at any time without
waiting for a query from the router. Host can also signal when they no longer
want to receive traffic for a specific group by sending a leave-group message.
These IGMP messages are used by the router to identify ports containing
multicast hosts and to restrict the downstream flow of multicast data to only
these ports. If more than one router on the LAN is performing IP multicasting,
one of these is elected as the “querier” and assumes the role of querying for
group members. It then propagates the service request up to any neighboring
multicast router to ensure that it will continue to receive the multicast service.
The following parameters are used to control Layer 3 IGMP and query functions.
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