From STP to RSTP
Classic 802.1D took 30-50 seconds to recover from a failure (listening, learning). Rapid STP (802.1w) converges in about a second: switches agree with a quick proposal/agreement handshake instead of waiting on timers. Cisco's Rapid PVST+ runs a separate RSTP tree for each VLAN.
| 802.1D state | RSTP state | Learns MACs? | Forwards? |
|---|---|---|---|
| Disabled / Blocking / Listening | Discarding | No | No |
| Learning | Learning | Yes | No |
| Forwarding | Forwarding | Yes | Yes |
| RSTP role | Meaning |
|---|---|
| Root | Best path to the root bridge |
| Designated | Forwards on its link (away from the root) |
| Alternate | Discarding; a ready backup path to the root (replaces 802.1D blocking) |
| Backup | Discarding; a spare designated port to the same shared segment (rare: hubs) |
| Link type | Meaning |
|---|---|
| Point-to-point (P2p) | Full duplex link to one switch: fast handshake allowed |
| Shared | Half duplex (a hub): falls back to slower behaviour |
| Edge | A port to an end device (PortFast): forwards at once, no BPDUs expected |
In NetLab
▶ SW2 SW2>enable SW2#configure terminal Enter configuration commands, one per line. End with CNTL/Z. SW2(config)#spanning-tree mode rapid-pvst SW2(config)#end *Mar 1 00:00:04.000: %SYS-5-CONFIG_I: Configured from console by console SW2#show spanning-tree summary | include mode|VLAN Switch is in rapid-pvst mode VLAN0001 0 0 0 3 3 SW2#show spanning-tree vlan 1 | include protocol Spanning tree enabled protocol rstp
Tip: The 802.1D timers still exist (Hello 2 s, Max Age 20 s, Forward Delay 15 s) and show up in the output, but RSTP rarely waits for them.
Common mistake:
spanning-tree mode rapid-pvstmust be set on every switch to get rapid convergence everywhere. Mixed modes still work, but the links to the old-mode switches converge slowly.