R3166-R3206-HP High-End Firewalls Network Management Configuration Guide-6PW101

Device Comparison process

BPDU of port

after com

arison

After comparison:

• 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.

• 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 Figure 27.

Figure 27 The final calculated spanning tree

NOTE:

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

The BPDU forwarding mechanism in STP

• 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.

• 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.

• 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.

• If a path becomes faulty, the root port on this path will no longer receive new configuration BPDUs

and the old configuration BPDUs will be discarded due to timeout. In this case, the device will