Performing The Calculation Process Of The Stp Algorithm - HP A5830 Configuration Manual

Upon initialization of a network, each device generates and periodically sends configuration BPDUs with
itself as the root bridge. After network convergence, only the root bridge generates and periodically
sends configuration BPDUs, and the other devices forward the BPDUs.
Root port
On a non-root bridge, the port nearest to the root bridge is the root port. The root port communicates with
the root bridge. Each non-root bridge has only one root port. The root bridge has no root port.
Designated bridge and designated port
Table 7 Description of designated bridges and designated ports
Classification
For a device
For a LAN
As shown in
BPDUs to Device B through port A1, the designated bridge for Device B is Device A, and the designated
port of Device B is port A1 on Device A. If Device B forwards BPDUs to the LAN, the designated bridge
for the LAN is Device B, and the designated port for the LAN is port B2 on Device B.
Figure 11 Schematic diagram of designated bridges and designated ports
Device B
Port B1
Port B2
Path cost
Path cost is a reference value used for link selection in STP. STP calculates path costs to select the most
robust links and block redundant links that are less robust, to prune the network into a loop-free tree.

Performing the calculation process of the STP algorithm

NOTE:
The spanning tree calculation process described in the following sections is a simplified process for
example only.
Designated bridge
A device directly connected with the
local device and responsible for
forwarding BPDUs to the local device
The device responsible for forwarding
BPDUs to this LAN segment
Figure 1 1, Device B and Device C are directly connected to a LAN. If Device A forwards
Device A
Port A1
Port A2
Port C1
Port C2
LAN
Designated port
The port through which the designated bridge
forwards BPDUs to this device
The port through which the designated bridge
forwards BPDUs to this LAN segment
Device C
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