Basic Concepts In Stp - HP FlexNetwork NJ5000 User Manual

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Root path cost
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Designated bridge ID (represented by device priority)
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Designated port ID (represented by port name)

Basic concepts in STP

Root bridge
A tree network must have a root bridge. The entire network contains only one root bridge, and all the
other bridges in the network are called "leaf nodes". The root bridge is not permanent, but can
change with changes of the network topology.
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. The other devices only 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
Classification
For a device
For a LAN
As shown in
BP2, and CP1 and CP2 are ports on Device A, Device B, and Device C, respectively.
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If Device A forwards BPDUs to Device B through AP1, the designated bridge for Device B is
Device A, and the designated port of Device B is port AP1 on Device A.
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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 the port BP2 on Device B.
Figure 157 Designated bridges and designated ports
Designated bridge
Device directly connected with the local
device and responsible for forwarding
BPDUs to the local device.
Device responsible for forwarding BPDUs
to this LAN segment.
Figure 157, Device B and Device C are connected to the LAN. AP1 and AP2, BP1 and
Designated port
Port through which the designated bridge
forwards BPDUs to the local device.
Port through which the designated bridge
forwards BPDUs to this LAN segment.
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