A single data MDT can transport one or more IPv4 (C-S, C-G) streams. This allows multiple multicast streams starting from the same VPRN going to the same set of leafs to utilize a single data MDT. Characteristics of an MDT include:
a multi-stream data MDT can carry IPv4 only
a multi-stream data MDT can co-exist with a single-group data MDT
a default MDT must be configured
To create a multi-stream MDT data, an MDA data policy must be configured in the context of MVPN on the source node. This policy maps multiple (C-S, C-G) streams to a single data MDT. Because this configuration is per MVPN, multiple VPNs can have identical policies configured, each for its own VPN context.
When a multicast stream is mapped to a multi-stream data MDT policy, the data will traverse the default MDT first. The data delay timer is used to switch the data from the default MDT to the multi-stream data MDT.
When the multi-stream data MDT is deleted, the traffic switches back to the default MDT.
In some cases when a new multi-stream data MDT is configured which is better suited, some streams might prefer this new multi-stream data MDT. To switch, the traffic will switch to the default MDT and then to the new multi-stream data MDT.
MDT data can be configured as SSM or ASM.
There can be multiple multi-stream policies assigned to a single data MDT configuration. In this case, the policy acts as a link list, the first (lowest index) matched multi-stream policy is used for that specific stream. The following are the rules of matching a multi-stream data MDT to (C-S, C-G) mapping on a source PE (in order):
The multi-stream policy is evaluated to enable the feature in service when per-(C-S, C-G) configuration is present, starting from the lowest numerical policy index (only entries that are not shutdown are evaluated). The first multi-stream data MDT (the lowest policy index) the (C-S, C-G) maps to is selected.
If (C-S, C-G) does not map to any of the multi-stream data MDTs, per-(C-S, C-G) single data MDTs are used if a (C-S, C-G) maps to an existing MDT based on data-thresholds.
The default MDT is used if no policy matches to a data MDT.
When a (C-S, C-G) arrives, it start on the default MDT but can switch to a data MDT when the data delay interval expires. It does not check the data-threshold before switching.
When going from one multi-stream data MDT to a more suitable one, the traffic will first switch to the default MDT and then switch to the new multi-stream data MDT based on the data-delay-interval.
When a data MDT tunnel fails, all (C-S, C-G)s using this multi-stream data MDT move to the default MDT, and the groups move back to the data MDT when it is restored.