Data MDT Characteristics

The maximum number of data MDTs for all VPNs on a PE router is 8000, and the maximum number of data MDTs for a VRF instance is 1024. The configuration of a VRF instance can limit the number of MDTs possible. No new MDTs can be created after the 1024 MDT limit is reached in the VRF instance, and all traffic for other sources that exceed the configured limit is sent on the default MDT.

Creation of data MDTs depends on the monitoring of the multicast source data rate. This rate is checked once per minute, so the creation of data MDTs can be delayed up to 1 minute after a source exceeds a configured limit. In the same way, if the source data rate falls below the configured value, data MDT deletion can be delayed for up to 1 minute until the next statistics-monitoring collection cycle.

Changes to the configured data MDT limit value do not affect existing tunnels that exceed the new limit. Data MDTs that are already active remain in place until the threshold conditions are no longer met.

To remove active data MDTs no longer included in a newly configured group address range, you must restart the PIM routing instance. This restart clears all remnants of the former group addresses but disrupts routing and therefore requires a maintenance window for the change.

Multicast tunnel (mt-) interfaces created because of exceeded thresholds are not re-created if the routing process crashes. Therefore, graceful restart does not automatically reinstate the data MDT state. However, as soon as the periodic statistics collection reveals that the threshold condition is still exceeded, the tunnels are quickly re-created.

Data MDTs are supported for customer traffic with PIM sparse mode, dense mode, and sparse-dense mode. Note that the provider core does not support PIM dense mode.