Configuration Guide User guide

BigIron RX Series Configuration Guide 359
53-1002484-04
Chapter
13
Configuring Rapid Spanning Tree Protocol
In this chapter
•Overview of Rapid Spanning Tree Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 359
•Edge ports and edge port roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
•Point-to-point ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
•Bridge port states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
•Edge port and non-edge port states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
•Changes to port roles and states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
•State machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
•Convergence in a simple topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
•Convergence in a complex RSTP topology . . . . . . . . . . . . . . . . . . . . . . . . . . 381
•Compatibility of RSTP with 802.1D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
•Configuring RSTP parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
•Displaying RSTP information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
Overview of Rapid Spanning Tree Protocol
RSTP provides rapid convergence and takes advantage of point-to point wiring of the spanning tree.
Failure in one forwarding path does not affect other forwarding paths. RSTP improves the operation
of the spanning tree while maintaining backward compatibility.
NOTE
The total number of supported STP, RSTP, or MSTP indices is 128.
Bridges and bridge port roles
A bridge in an RSTP rapid spanning tree topology is assigned as the root bridge if it has the highest
priority (lowest bridge identifier) in the topology. Other bridges are referred to as non-root bridges.
Unique roles are assigned to ports on the root and non-root bridges. Role assignments are based
on the following information contained in the BPDU (RSTp packet):
• Root bridge ID
• Path cost value
• Transmitting bridge ID
• Designated port ID