SPB-PIM Gateway Controller Node

SPB-PIM Gateway Controller Node (Controller) shares stream information between the local SPB domain and a foreign domain. The foreign domain is the PIM network Rendezvous point (RP) or another SPB domain Controller.

The Controller functionality is outlined below:
  • The Controller discovers PIM sources for a specific multicast group and distributes them to the Gateways.
    Note

    Note

    PIM source discovery is either through MSDP or static configuration of foreign streams at the Controller.

  • The Controller advertises local SPB originated streams through MSDP to another PIM domain or another SPB domain.

  • The Controller refrences the Unicast IP route table to determine which Gateway has the best route to the PIM source. The Controller then assigns the stream to the selected Gateway.

The Controller Node has the following components:

  • Source Discovery (MSDP and static configuration)

  • Gateway Selection Controller

Source Discovery (MSDP and static configuration)

MSDP resides in the Controller BEB or Controller BCB and PIM network RP that wish to advertise multicast source information between domains.

You can implement SPB-PIM GW under the following scenarios:

  • The multicast source resides in the Protocol Independent Sparse Module (PIM-SM) domain. The multicast source must be discovered by MSDP residing on the Gateway Controller in the SPB domain.

  • The multicast source resides in the SPB domain. The multicast source must be advertised to the neighboring PIM domain through MSDP peers.

For more information on MSDP, see MSDP overview.
Note

Note

You can also configure multicast sources statically on the Controller. Static configuration is useful for SSM multicast group range streams in the foreign domain, which are not advertised by MSDP. Static configuration is also useful for when two SPB domains are connected through a PIM Gateway, and want to only advertise a subset of streams to each other, without enabling MSDP.

Gateway Selection Controller

The Gateway Selection Controller resides in the Controller BEB or Controller BCB node in the SPB network. The Gateway Selection Controller receives source information from MSDP or through static configuration. The source information consists of the following components:

  • Sender IP address (S)

  • Group IP address (G)

  • VRF ID of the stream

  • RP of the source (optional)

Gateway Selection Controller finds the best BEB (Gateway Node) in the SPB network through which the sender sends traffic to group G. The Gateway Selection Controller performs the following tasks:

  • The Gateway Selection Controller uses Layer 3 reachability information to reach S, which is retrieved from the ISIS IP Shortcuts (IPSC) database.

  • The VSN identifier (ISID) is determined by using the VRF ID provided by MSDP.

  • The Gateway Selection Controller uses the VRF ID and searches the IP shortcut database to determine which Gateway is closest to S.
    Note

    Note

    If multiple BEBs have a route to S, the BEB with the lowest Layer 3 metric is selected as the Gateway.

    Note

    Note

    If a Gateway link fails or the cost of the route changes, the selection process identifies the link failure as a route change and selects another best Gateway BEB.

The selected Gateway BEB for a stream must satisfy the following criteria:
  • The selected Gateway BEB for a stream must announce a route to the source of the foreign stream through ISIS.
    Note

    Note

    Among all the routes to the source of the foreign stream announced by different BEBs through ISIS, the route announced by the selected Gateway has the longest prefix match and has the lowest external route metric.

  • If multiple BEBs meet the Gateway selection criteria, a deterministic hash function of system ID, source IP address, and group IP address is used. The deterministic hash function is computed for each of the BEBs that meet the Gateway selection criteria. The BEB that generates the lowest hash value is selected as the Gateway for the stream.

The result of the Gateway selection process is saved in the Gateway assignment table. The Gateway assignment table consists of VSN identifier or ISID, S, G, and the selected Gateway BEB. Having only one selected Gateway BEB ensures that traffic from source S is drawn into the SPB network by only one BEB, the selected Gateway BEB. The selection Controller then distributes the Gateway assignment table information to all the Gateway nodes.
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