User Manual UMN:CLI
V5808
293
If low BPDU is received from the root switch or the designated switch, it is immediately
accepted. For example, suppose that the root switch is disconnected from the switch B in
the figure below. Then, the switch B is considered to be the root due to the disconnection,
and it forwards BPDU.
In this case, the switch C transmits BPDU including the root information to the switch B.
Thus, SWITCH B configures a port connected to SWITCH C as the new root port.
Fig. 8.16 Example of Receiving Low BPDU
8.3.2.3 Rapid Network Convergence
In the figure below, a new link is connected between SWITCH A and the root. Root and
SWITCH A are not directly connected, but indirectly connected through SWITCH D. After
SWITCH A is newly connected to the root, packets cannot be transmitted between the
ports because the state of two switches becomes listening, and no loop is created.
In this state, if the root transmits BPDU to SWITCH A, SWITCH A transmits new BPDU to
SWITCH B and SWITCH C, then SWITCH C transmits new BPDU to SWITCH D.
SWITCH D, which received BPDU from SWITCH C, turns the port connected to SWITCH
C into blocking state to prevent the loop after the new link.
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