Each SPBM network instance is associated with at least one backbone VLAN (B-VLAN) in the core SPBM network.
Note
SPB internally uses spanning tree group (STG) 63 or Multiple Spanning Tree Instance (MSTI) 62. STG 63 or MSTI 62 cannot be used by another VLAN or MSTI. For non-SPB customer networks, if you use STG 63 or MSTI 62 in the configuration, you must delete STG 63 or MSTI 62 before you can configure SPBM.
This VLAN is used for both control plane traffic and dataplane traffic.
Note
Always configure two B-VLANs in the core to allow load distribution over both B-VLANs.
SPBM alters the behavior of the VLAN. When a B-VLAN is associated with an SPBM network the following VLAN attributes and behaviors are modified for the B-VLAN:
Flooding is disabled
Broadcasting is disabled
Source address learning is disabled
Unknown MAC discard is disabled
You cannot add ports to a B-VLAN manually, IS-IS enabled ports are automatically added to the B-VLAN.
Essentially the BMAC addresses are programmed into the B-VLAN Forwarding Information Bases (FIBs) by IS-IS instead of the traditional VLANs flooding and learning approach.
Modification of the VLAN behavior is necessary to ensure proper control over the SPBM traffic.