Local-Area Networks and LAN Switching - CCIE Routing and Switching Exam Certification Guide - page 132

STP Figure 4-16

forwarding

blocking

forwarding

blocking

The router interface priority can be changed with the priority keyword, with priority values
ranging from 1 to 255:

R4(config-if)#bridge-group 1 priority ?
<0-255>

Bridge Identifier (BID) and Path Costs
As shown in Figure 4-17, the BID is 8 bytes long and contains a bridge priority (2 bytes), along
with one of the bridge's MAC addresses (6 bytes). With 2 bytes, the priority values range from
0 to 65,535. The default priority is 32,768.

BID Format Figure 4-17

Bridge Priority
2 bytes

MAC Address
6 bytes

Each port is assigned a Port ID. Port IDs are 16 bits long and consist of two parts: a 6-bit priority
setting and a 10-bit port number.