When a local LAN running spanning tree protocol connecting to TRILL
campus via more than one RBridge, there are several ways to perform
loop avoidance. One of them illustrated by RFC6325 [RFC6325] A.3 was
to make relevant ports on edge RBridges involving in spanning tree
calculation. When edge RBridges are emulated as a single highest
priority root, the local bridged LAN will be naturally partitioned
after running spanning tree protocol. This approach achieves better
link utilization and intra-VLAN load balancing in some scenarios.
This document describes how the edge RBridges react to topology
change occurring in bridged LAN in order to make the abovementioned
spanning tree approach function correct.