6–6
MULTINET4 MULTI-PORT SERIAL SERVER & MANAGED SWITCH – INSTRUCTION MANUAL
OPERATIONAL GUIDE
CHAPTER 6: OPERATIONAL GUIDE
FIGURE 6–2: Port Roles in a Rapid Spanning Tree Network
6.3.1.1 BPDUs
The messages exchanged by the bridges are special data frames called Bridge Protocol
Data Units (BPDUs). The BPDUs contain identifying information and information about the
root
path cost
. The best path from a bridge to the root has the lowest path cost. (The
measurement takes into account the bandwidth on intervening segments.) When the
spanning tree is being calculated the bridges exchange configuration BPDUs. Other types
of BPDUs are exchanged during normal operation.
Multinet4 supports a choice of
cost style
.
6.3.1.2 Bridge Roles
Each configured spanning tree has a single root bridge. All other bridges active in the
system are
designated bridges
. For each segment the connected bridge that provides
the shortest path to the root bridge is that segment’s designated bridge.
6.3.1.3 Port Roles
After convergence each port in the tree is assigned one of four roles:
