Specifications

CHAPTER 3
Spanning Tree
Spanning Tree Port States
When a port is first activated, it transitions through the following stages shown in Table 3-2.
Table 3-2 Spanning Tree Port States
Port State Timer Action
Blocking Max Age (20 sec) Discards frames, does not learn MAC addresses, receives BPDUs
Listening Forward Delay (15 sec) Discards frames, does not learn MAC addresses, receives BPDUs to determine its
role in the network
Learning Forward Delay (15 sec) Discards frames, does learn MAC addresses, receives and transmits BPDUs
Forwarding Accepts frames, learns MAC addresses, receives and transmits BPDUs
Per-VLAN Spanning-Tree
The IEEE’s version of STP assumes one common Spanning-tree instance (and thus one root bridge) regardless of how
many VLANs are configured. With the Cisco Per-VLAN Spanning-Tree (PVST+) there is a different instance of STP for
each VLAN. To derive the VLAN BID, the switch picks a different MAC address from its base pool for each VLAN.
Each VLAN has its own root bridge, root port, and so on. You can configure these so that data flow is optimized, and
traffic load is balanced among the switches by configuring different root bridges for groups of VLANs.
PVST+ is enabled by default on Cisco switches.
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue
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