88 
Device Comparison process 
Configuration BPDU 
on ports after 
comparison 
Device C 
Port C1 performs the following operations:  
1.  Receives the configuration BPDU of Port A2 {0, 0, 0, 
Port A2}.  
2.  Determines that the received configuration BPDU is 
superior to its existing configuration BPDU {2, 0, 2, 
Port C1}.  
3.  Updates its configuration BPDU. 
Port C2 performs the following operations: 
1.  Receives the original configuration BPDU of Port B2 
{1, 0, 1, Port B2}.  
2.  Determines that the received configuration BPDU is 
superior to the existing configuration BPDU {2, 0, 2, 
Port C2}.  
3.  Updates its configuration BPDU. 
•  Port C1: {0, 0, 0, Port 
A2} 
•  Port C2: {1, 0, 1, Port 
B2} 
Device C performs the following operations:  
1.  Compares the configuration BPDUs of all its ports.  
2.  Decides that the configuration BPDU of Port C1 is the 
optimum.  
3.  Selects Port C1 as the root port with the configuration 
BPDU unchanged. 
Based on the configuration BPDU and path cost of the root 
port, Device C calculates the configuration BPDU of Port C2 
{0, 10, 2, Port C2}. Device C compares it with the existing 
configuration BPDU of Port C2 {1, 0, 1, Port B2}. Device C 
determines that the calculated configuration BPDU is 
superior to the existing one, selects Port C2 as the 
designated port, and replaces the configuration BPDU of 
Port C2 with the calculated one. 
•  Root port (Port C1): 
{0, 0, 0, Port A2} 
•  Designated port (Port 
C2): {0, 10, 2, Port 
C2} 
Port C2 performs the following operations: 
1.  Receives the updated configuration BPDU of Port B2 
{0, 5, 1, Port B2}.  
2.  Determines that the received configuration BPDU is 
superior to its existing configuration BPDU {0, 10, 2, 
Port C2}.  
3.  Updates its configuration BPDU. 
Port C1 performs the following operations:  
1.  Receives a periodic configuration BPDU {0, 0, 0, Port 
A2} from Port A2.  
2.  Determines that it is the same as the existing 
configuration BPDU.  
3.  Discards the received BPDU. 
•  Port C1: {0, 0, 0, Port 
A2} 
•  Port C2: {0, 5, 1, Port 
B2}