Specifications

CHAPTER 3
Spanning Tree
Spanning Tree Election Criteria
Spanning Tree builds paths out from a central point along the fastest available links. It selects paths according to the
following criteria:
n Lowest root bridge ID (BID)
n Lowest path cost to the root
n Lowest sender bridge ID
n Lowest sender port ID (PID)
When reading the path selection criteria, remember the following:
n Bridge ID: Bridge priority: Bridge MAC address.
n Bridge priority: 2-btye value, 0–65,535 (0–0xFFFF).
n Default priority: 32,768 (0x8000).
n Port ID: Port priority: port number.
n Port priority: A 6-bit value, 0–63, default is 32.
n Path cost: This is the cumulative value of the cost of each link between the bridge and the root. Cost values were
updated in 2000, and you should see only new cost values, but both are given in the following table (see Table 3-1).
Old and new switches work together.
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue