MLD Explicit Host Tracking Overview

Explicit host tracking enables the router to explicitly track each individual host that is joined to a group or channel on a particular multi-access network.

Explicit host tracking provides the following benefits:

When the router is configured for explicit host tracking and starts performing immediate leave using the host information collected, every leave message received for a group or channel is treated as follows:

You can enable Multicast Listener Discovery (MLD) explicit host tracking on an interface only if MLD V1 or V2 has been previously enabled on the interface. Explicit host tracking is not enabled by default when you enable MLD on the interface. Explicit host tracking cannot be configured on passive MLD interfaces.

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 is enabled on an MLD V2 interface, even if a group has to downgrade to MLD V1 due to the presence of an MLD V1 host, explicit host tracking continues for that group. To avoid this, you can use the disable-if-mld-v1-detected keyword. If you select this option, the router turns off explicit host tracking for the group when MLD V1 host reports are received for the group on that interface. This option does not have any significance on an interface configured for MLD V1 and is ignored if selected.

If you execute the command on an interface that was previously enabled for immediate-leave, the configuration is accepted, immediate-leave is turned off and an appropriate warning message logged. Any attempt to configure immediate-leave on an interface that has explicit host tracking enabled is rejected and an error message logged.

Related Documentation