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At a media studio, a network operations engineer wants the authorized distribution pair to remain Rapid PVST+ root for VLAN 196 even if an access-layer switch advertises a superior bridge ID. Which safeguard fits?
Root guard keeps an unexpected superior BPDU from changing the intended root hierarchy on the protected designated segment. It can place the receiving port into root-inconsistent state.
BPDU guard is appropriate on endpoint edges, not every legitimate switch-to-switch link carrying BPDUs.
802.1Q VLAN tags do not stop Layer 2 loops within each VLAN.
PortFast bypasses some transition behavior on edge ports; core trunks should participate normally in STP.
At a satellite office, the migration lead has a redundant inter-switch link in VLAN 126. A failure can make a blocked/root port stop receiving BPDUs without losing electrical carrier. Which STP feature best reduces loop risk?
Loop guard helps prevent a root/alternate port from transitioning incorrectly to forwarding when superior BPDUs stop arriving on VLAN 126.
PortFast is intended for true edge connections, not to solve a transit-link BPDU interruption.
Identical priorities and absent STP protection do not preserve topology safety after BPDU loss.
DHCP snooping protects address assignment, not bridge control-plane BPDU receipt.
At a payment processor, a network administrator reviews Rapid PVST+ port roles in VLAN 48 after a topology change. Which statement accurately distinguishes a root port from a designated port?
Rapid PVST+ computes roles per VLAN 48: the root bridge has designated forwarding ports, while each non-root bridge chooses one best root port. Alternate ports offer blocked standby paths.
The root bridge has no root port because its own root path cost is zero.
An alternate role supplies redundancy and does not forward normal user traffic while discarding.
Port status and root bridge election use bridge/path IDs, not a simple physical interface number comparison.
At a bank branch, the branch support lead is validating Rapid PVST+ convergence for VLAN 188 and inspects the discarding, learning and forwarding states. Which state description is correct?
RSTP states separate discarding, learning and forwarding; frame forwarding occurs in the forwarding state, and learning can build a MAC table before traffic forwarding for VLAN 188.
Learning intentionally observes source MACs but does not yet forward ordinary user frames.
A forwarding port continues normal STP BPDU participation and can learn MACs.
Discarding prevents normal data forwarding; that is the basis for loop prevention.
At an enterprise data center, a network administrator must identify the Rapid PVST+ root for VLAN 45; all listed switches are on the same Layer 2 topology and no superior external BPDU exists. Which switch wins?
SW-3 has bridge priority 4096; root selection compares bridge ID priority first and MAC as tie-breaker. It wins because this is the lowest priority in the presented candidates.
SW-2 has bridge priority 32768; root selection compares bridge ID priority first and MAC as tie-breaker. The winning bridge has lower priority 4096, so this cannot be root despite its MAC value.
SW-4 has bridge priority 12288; root selection compares bridge ID priority first and MAC as tie-breaker. The winning bridge has lower priority 4096, so this cannot be root despite its MAC value.
SW-1 has bridge priority 24576; root selection compares bridge ID priority first and MAC as tie-breaker. The winning bridge has lower priority 4096, so this cannot be root despite its MAC value.
At a biotech lab, an implementation partner examines four ports on a non-root Rapid PVST+ switch for VLAN 192. Their received BPDUs identify the same root bridge but yield different total path costs. Which port becomes the root port?
Root-port selection begins with the lowest accumulated path cost toward the root bridge. Gi1/0/1 has cost 19; it is preferred, assuming equal root IDs and no other superior tie-breakers.
Root-port selection begins with the lowest accumulated path cost toward the root bridge. Gi1/0/4 has cost 35; cost 19 is better than 35, so this path is not selected.
Root-port selection begins with the lowest accumulated path cost toward the root bridge. Gi1/0/3 has cost 29; cost 19 is better than 29, so this path is not selected.
Root-port selection begins with the lowest accumulated path cost toward the root bridge. Gi1/0/2 has cost 23; cost 19 is better than 23, so this path is not selected.
Access port Gi1/0/20 in VLAN 130 is configured for PortFast and BPDU guard. An unauthorized mini-switch is connected and begins sending BPDUs. Which immediate reaction is expected under the configured guard policy?
On a BPDU-guarded PortFast edge Gi1/0/20, unexpected BPDUs normally trigger err-disable to avoid unintended switching loops in VLAN 130. The underlying cause must be addressed before recovery.
BPDU guard is an edge protection, not an STP root-port promotion mechanism.
A received BPDU does not automatically authorize IOS to transform an access port into a trunk.
The guard does not change VLAN database segmentation to merge different broadcast domains.
Four switches start Rapid PVST+ on VLAN 131; no root has yet been elected and no external BPDU is superior. Which candidate has the best bridge priority and becomes root?
The bridge with the lowest STP priority wins the root election for VLAN 131, with MAC used only as a tie-break. 0 is the lowest listed priority.
The bridge with the lowest STP priority wins the root election for VLAN 131, with MAC used only as a tie-break. This 28672 is higher than winning priority 0.
The bridge with the lowest STP priority wins the root election for VLAN 131, with MAC used only as a tie-break. This 20480 is higher than winning priority 0.
The bridge with the lowest STP priority wins the root election for VLAN 131, with MAC used only as a tie-break. This 24576 is higher than winning priority 0.
A non-root Rapid PVST+ switch has four possible uplinks toward the same VLAN 132 root. Each receives the same root bridge ID. Which port is chosen based on the measured total costs?
Root-port selection chooses the lowest total path cost among ports advertising the same root bridge. This path cost 4 is the least.
Root-port selection chooses the lowest total path cost among ports advertising the same root bridge. The alternative cost 4 is lower than 32.
Root-port selection chooses the lowest total path cost among ports advertising the same root bridge. The alternative cost 4 is lower than 27.
Root-port selection chooses the lowest total path cost among ports advertising the same root bridge. The alternative cost 4 is lower than 20.
An access port Gi1/0/23 is configured for PortFast and receives an unexpected BPDU from an attached unmanaged switch. The operator wants BPDU guard only on this interface, not as a switchwide default. Which IOS command meets that scope?
Interface-level BPDU guard protects this specific access port, sending it to err-disabled if a BPDU arrives. A global default would affect all eligible PortFast access ports.
PortFast accelerates the edge transition but does not by itself guarantee err-disable on an unexpected BPDU.
Root guard blocks superior-root influence but is not the explicit BPDU guard trigger requested for any BPDU.
BPDU filtering suppresses protocol BPDUs and can conceal an unauthorized switch, rather than err-disabling the port on receipt.
In VLAN 134, SW-A and SW-B both advertise configured bridge priority 4096. Their MAC addresses are SW-A 00:11:22:00:00:20 and SW-B 00:11:22:00:00:05. No switch advertises a lower priority. Which switch becomes the Rapid PVST+ root and why?
STP compares full bridge IDs: the priority (including VLAN system ID) ranks first; with equal priority, the numerically lower MAC address wins the root election.
When priorities tie, STP selects the smaller MAC address, not the larger one.
A single spanning-tree instance has one root bridge; an ID tie is resolved deterministically.
Port count is not part of the bridge ID comparison.
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