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200-150 · Question #52

Switch A has BPDU fitering configured on all active interfaces. A second switch, Switch B, is connected to Switch A. Which two actions will Switch A take when Switch B is connected to it? (Choose…

The correct answer is A. Switch A will not send any BPDUs. C. Switch A will not accept any BPDUs. When BPDU filtering is enabled at the interface level, the port unconditionally suppresses both outbound and inbound BPDUs, removing that port from STP participation entirely.

Cisco Data Center Networking Technologies

Question

Switch A has BPDU fitering configured on all active interfaces. A second switch, Switch B, is connected to Switch A. Which two actions will Switch A take when Switch B is connected to it? (Choose two.)

Options

  • ASwitch A will not send any BPDUs.
  • BSwitch A will transition the port a normal spanning tree port.
  • CSwitch A will not accept any BPDUs
  • DSwitch A will errdisable the port.
  • ESwitch A will start sending BPDUs to Switch B.

How the community answered

(49 responses)
  • A
    76% (37)
  • B
    4% (2)
  • D
    14% (7)
  • E
    6% (3)

Why each option

When BPDU filtering is enabled at the interface level, the port unconditionally suppresses both outbound and inbound BPDUs, removing that port from STP participation entirely.

ASwitch A will not send any BPDUs.Correct

Interface-level BPDU filtering (spanning-tree bpdufilter enable) prevents the switch from transmitting BPDUs out of the configured port unconditionally, unlike global BPDU filtering which can revert upon receiving a BPDU.

BSwitch A will transition the port a normal spanning tree port.

Transitioning back to a normal STP port upon receiving a BPDU is the behavior of globally configured BPDU filtering, not interface-level BPDU filtering, which has no such fallback mechanism.

CSwitch A will not accept any BPDUsCorrect

Interface-level BPDU filtering also causes the port to silently drop any received BPDUs, so Switch A will not process or react to BPDUs sent by Switch B on that interface.

DSwitch A will errdisable the port.

Errdisabling the port is the action taken by BPDU Guard, not BPDU filtering - BPDU Guard shuts down a PortFast port when any BPDU is received.

ESwitch A will start sending BPDUs to Switch B.

BPDU filtering specifically prevents the transmission of BPDUs on configured interfaces, so Switch A will not send any BPDUs to Switch B.

Concept tested: STP BPDU filtering interface-level vs global behavior

Source: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/12-2_55_se/configuration/guide/3750xscg/swstpopt.html

Topics

#BPDU filtering#spanning tree#STP port behavior#switch interoperability

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