Each SPBM network instance is associated with at least one backbone VLAN (B-VLAN) in the core SPBM network.
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 MAC address learning is disabled
Unknown MAC discard is enabled
Ports cannot be added to a B-VLAN manually, IS-IS takes care of adding ports to the B-VLAN.
Essentially the B-MAC 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.