Cisco WS-C2980G-A Software Guide - Page 113

Chapter 7 Configuring Spanning Tree Understanding How MST Works RSTP Port States The port state controls the forwarding and learning processes and provides the values of discarding, learning, and forwarding. Table 7-3 provides a comparison between STP port states and RSTP port states. Table 7-3 Comparison Between STP and RSTP Port States Operational Status Enabled STP Port State Blocking1 RSTP Port State Port Included in Active Topology? Discarding2 No Enabled Listening Discarding No Enabled Learning Learning Yes Enabled Forwarding Forwarding Yes Disabled Disabled Discarding No 1. IEEE 802.1D port state designation. 2. IEEE 802.1w port state designation. Discarding is analogous with, and the same as blocking in MST in this document. In a stable topology, RSTP ensures that every root port and designated port transition to forwarding while all alternate ports and backup ports are always in the discarding state. MST-to-SST Interoperability A virtual bridged LAN may contain interconnected regions of SST and MST bridges. Figure 7-8 shows this relationship. Figure 7-8 Network with Interconnected SST and MST Regions MST Region r B F B B B F r SST Region b r r F F/f = Forwarding B/b = Blocking R = Root Bridge r = Root port F F F FR F F MST Region FF F r F r r b SST Region B 68285 78-15486-01 Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide-Release 8.1 7-17