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Data MDT Sources

A C-SG flow arriving in the source VRF is a candidate for a data MDT if the system matches the C-SG in the route map that you specify for the data MDT using the ip pim data-mdt command. The C-SG flow is initially forwarded on the default MDT. The system creates the data MDT when the flow rate exceeds a value you configure in the route map using the set threshold command.

When the Source C-PIM-SM first creates a data MDT for a C-SG flow, it sends a <C-SG, P-G> MDT join message with type, length, value (TLV) format to the default MDT. This message invites peer PE routers to join the new data MDT. It starts a timer that you can configure using the mdt-data-delay command to track the number of seconds before switching to the data MDT. When that timer expires, C-PIM-SM switches from sending C-SG data on the default MDT to sending data on the data MDT.

When the C-SG flow is switched to the data MDT, the Source C-PIM-SM starts a timer that you can configure using the mdt-data-holddown command to track the number of seconds before switching to the default MDT. When the timer expires, the data MDT is deleted and the C-SG flow switched back to the default MDT if the flow rate drops back below the threshold. If the flow rate exceeds the threshold, the timer restarts. If the timer expires and the flow rate is below the threshold, the data MDT is removed.

The Source C-PIM-SM maintains sent MDT Join TLV messages in its database as long as they are active. While the data MDT is active, C-PIM-SM resends that MLD Join TLV message using a setting that you can configure using the mdt-interval command to measure time in seconds between successive MLD join TLV messages.

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