Juniper JUNOSE 11.0.X MULTICAST ROUTING Configuration Manual page 81

If one or more hosts that support only IGMP V1 are present on a network, the leave
latencies for the multicast groups to which those hosts are joined revert to the IGMP
V1 leave latency. This affects only the multicast groups to which these legacy hosts
are actually joined at any point in time.
You cannot configure explicit host tracking on passive IGMP interfaces or on IGMP
V1 interfaces. When you enable IGMP V2 or V3 on an interface, explicit host tracking
is not enabled by default.
When you enable explicit host tracking on an interface that has a membership state,
the router does not immediately start performing immediate leave. For a maximum
of group membership interval seconds, the router only performs host tracking. Any
leave messages that the router receives during this period receive normal leave
processing. Any leave messages received after this interval has elapsed receive
immediate leave processing, when appropriate.
When explicit host tracking has been enabled on an IGMP V3 interface, even if a
group has to downgrade to IGMP V2 due to the presence of an IGMP V2 host, explicit
host tracking continues for that group. To avoid this, you can use the
disable-if-igmp-v2-detected keyword. If you select this option, the router turns off
explicit host tracking for the group when IGMP V2 host reports are received for the
group on that interface. This option does not have any significance on an interface
configured for IGMP V2 and is ignored if provided. Because IGMP V1 does not support
leave messages, explicit host tracking is turned off for a group that downgrades to
IGMP V1 due to the presence of IGMP V1 hosts.
Explicit host tracking cannot be enabled on an interface that has immediate-leave
configured and vice versa. Any attempt to configure immediate-leave on an interface
that has explicit host tracking enabled or to configure explicit host tracking on an
interface that has immediate-leave enabled is rejected and an error message logged
on the screen.
The following example enables IGMP V3 explicit host tracking on interface 3/0.101
with the default configuration where the router continues to perform explicit host
tracking for IGMP V2 groups. To override this default configuration, you must use
the ip igmp explicit-tracking disable-if-igmp-v2-detected command.
ip igmp explicit-tracking
If the host sending the leave message is not the only host receiving traffic for
that group or channel, the router removes the host from the list of hosts on that
interface, but keeps the interface in the outgoing interface list for the multicast
group or channel. No group or group-source-specific queries are sent.
interface 3/0.101
ip igmp version 3
ip igmp explicit-tracking
end
Use to set explicit host tracking for IP IGMP interfaces.
To disable explicit host tracking if IGMP V2 hosts are detected, use the
disable-if-igmp-v2-detected keyword.
Example
Chapter 2: Configuring IGMP
Configuring Explicit Host Tracking
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