The GigE MAN portion of the network is implemented with traditional switches. Using MSTP running on individual switches facilitates redundancy in this part of the network. To provide dual homing of all VPLS services accessing from this part of the network, the VPLS PEs must participate in MSTP.
This can be achieved by configuring M-VPLS on VPLS-PEs (only PEs directly connected to the GigE MAN network), then assigning different managed-VLAN ranges to different MSTP instances. Typically, the M-VPLS would have SAPs with null encapsulations (to receive, send, and transmit MSTP BPDUs) and a mesh SDP to interconnect a pair of VPLS PEs.
Different access scenarios are displayed in Figure 1 as an example of network diagrams dually connected to the PBB PEs:
Access Type A — Source devices connected by null or dot1q SAPs
Access Type B — One QinQ switch connected by QinQ/801ad SAPs
Access Type C — Two or more ES devices connected by QinQ/802.1ad SAPs
Figure 1. Access resiliency
The following mechanisms are supported for the I-VPLS:
STP/RSTP can be used for all access types.
M-VPLS with MSTP can be used as is just for access type A. MSTP is required for access type B and C.
LAG and MC-LAG can be used for access type A and B.
Split-horizon-group does not require residential.
PBB I-VPLS inherits current STP configurations from the regular VPLS and M-VPLS.