Juniper ACX1000 Configuration Manual page 538

ACX Series Universal Access Router Configuration Guide
Overview and Topology
480
PIM-SM
PIM-SSM
IGMP snooping controls multicast traffic in a switched network. When IGMP snooping is
not enabled, the Layer 2 device broadcasts multicast traffic out of all of its ports, even
if the hosts on the network do not want the multicast traffic. With IGMP snooping enabled,
a Layer 2 device monitors the IGMP join and leave messages sent from each connected
host to a multicast router. This enables the Layer 2 device to keep track of the multicast
groups and associated member ports. The Layer 2 device uses this information to make
intelligent decisions and to forward multicast traffic to only the intended destination
hosts.
This example includes the following statements:
—Enables the Layer 2 device to actively filter IGMP packets to reduce load on the
proxy
multicast router. Joins and leaves heading upstream to the multicast router are filtered
so that the multicast router has a single entry for the group, regardless of how many
active listeners have joined the group. When a listener leaves a group but other listeners
remain in the group, the leave message is filtered because the multicast router does
not need this information. The status of the group remains the same from the router's
point of view.
—When only one IGMP host is connected, the
immediate-leave
statement enables the multicast router to immediately remove the group membership
from the interface and suppress the sending of any group-specific queries for the
multicast group.
When you configure this feature on IGMPv2 interfaces, ensure that the IGMP interface
has only one IGMP host connected. If more than one IGMPv2 host is connected to a
LAN through the same interface, and one host sends a leave message, the router
removes all hosts on the interface from the multicast group. The router loses contact
with the hosts that properly remain in the multicast group until they send join requests
in response to the next general multicast listener query from the router.
When IGMP snooping is enabled on a router running IGMP version 3 (IGMPv3) snooping,
after the router receives a report with the type BLOCK_OLD_SOURCES, the router
suppresses the sending of group-and-source queries but relies on the Junos OS
host-tracking mechanism to determine whether or not it removes a particular source
group membership from the interface.
—Enables you to change the number of IGMP messages sent on the
query-interval
subnet by configuring the interval at which the IGMP querier router sends general
host-query messages to solicit membership information.
By default, the query interval is 125 seconds. You can configure any value in the range
1 through 1024 seconds.
query-last-member-interval
device to detect the loss of the last member of a group.
—Enables you to change the amount of time it takes a
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immediate-leave