3com S7906E Manuel De Montage

 

1-8 

After comparison: 

z

 

Because the root path cost of CP2 (9) (root path cost of the 
BPDU (5) plus path cost corresponding to CP2 (4)) is smaller 
than the root path cost of CP1 (10) (root path cost of the 
BPDU (0) + path cost corresponding to CP2 (10)), the BPDU 
of CP2 is elected as the optimum BPDU, and CP2 is elected 
as the root port, the messages of which will not be changed. 

z

 

After comparison between the configuration BPDU of CP1 
and the calculated designated port configuration BPDU, port 
CP1 is blocked, with the configuration BPDU of the port 
unchanged, and the port will not receive data from Device A 
until a spanning tree calculation process is triggered by a new 
event, for example, the link from Device B to Device C going 
down. 

Blocked port CP2: 
{0, 0, 0, AP2} 
Root port CP2:  
{0, 5, 1, BP2} 

 

After the comparison processes described in the table above, a spanning tree with Device A as the root 
bridge is established as shown in 

. 

The final calculated spanning tree  

AP1

AP2

Device A

With priority 0

Device B

With priority 1

Device C

With priority 2

BP1

BP2

CP2

5

4

 

 

The spanning tree calculation process in this example is only simplified process. 

 

z

 

Upon network initiation, every switch regards itself as the root bridge, generates configuration 
BPDUs with itself as the root, and sends the configuration BPDUs at a regular hello interval. 

z

 

If it is the root port that received a configuration BPDU and the received configuration BPDU is 
superior to the configuration BPDU of the port, the device increases the message age carried in the 
configuration BPDU following a certain rule and starts a timer to time the configuration BPDU while 
sending out this configuration BPDU through the designated port. 

z

 

If the configuration BPDU received on a designated port has a lower priority than the configuration 
BPDU of the local port, the port immediately sends out its own configuration BPDU in response.