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Layer 3 IGMP (Query used with Multicast Routing)
IGMP Snooping – IGMP Snooping is a Layer 2 function (page 3-171) 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 switch 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 “Configuring
IGMP Snooping and Query Parameters” on page 3-171.)
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 3-176).
Note:
Layer 2 snooping and query is disabled if Layer 3 IGMP is enabled.
Configuring IGMP Interface Parameters
This 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.
Command Attributes
• VLAN (Interface) – VLAN interface bound to a primary IP address.
(Range: 1-4093)
• IGMP Protocol Status (Admin Status) – Enables IGMP on a VLAN interface.
(Default: Disabled)
L3 - network core
multicast routing
and L3 IGMP query
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