Working mechanisms

To forward Layer 2 traffic between customer sites across an SPBM network, you must configure Ethernet service instances on BEBs' customer network ports, and map Ethernet service instances to SPB VSIs.

SPBM uses ISIS-SPB in the control plane to calculate shortest path trees. It uses IEEE 802.1ah PBB encapsulation in the data plane to encapsulate and forward traffic.

SPBM uses the following generic process to calculate SPTs and forward traffic:

1. BEBs and BCBs send ISIS-SPB P2P hellos to establish and maintain adjacencies.

2. Adjacent nodes send LSPs to advertise their respective topology data. Eventually, the LSDBs of all nodes are synchronized.

3. Each node selects the forwarding path:

   1. Each node runs SPF to calculate the shortest path from itself to each of the other nodes.

   2. If equal-cost paths are available, each node runs ECT to choose the best forwarding path.

   3. The nodes populate their respective FDB and FIB tables with the forwarding path.

4. BEBs establish PWs over the SPBM network for transmitting customer traffic.