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Network Infrastructure and Connectivity →hardMultiple ChoiceObjective-mapped

Quick Answer

The correct action is to configure the interface as a trunk port and disable spanning-tree BPDU guard. This resolves the err-disabled state because the access switch’s port was likely configured with PortFast, which assumes an end host is connected; when the new switch sends BPDUs, BPDU guard immediately error-disables the port to prevent a potential bridging loop. On the CCNA 200-301 v2 exam, this scenario tests your understanding of how BPDU guard interacts with PortFast and why connecting a switch to a PortFast-enabled access port triggers the violation. A common trap is assuming the cable is faulty or that auto-negotiation must be disabled, but the real issue is the security feature misapplied to a switch-to-switch link. Remember the memory tip: “PortFast expects a host, not a switch—disable BPDU guard or face the err-disable glitch.”

CCNA Network Infrastructure and Connectivity Practice Question

This 200-301 practice question tests your understanding of network infrastructure and connectivity. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

Exhibit

SwitchA# show interfaces gigabitethernet 0/1
GigabitEthernet0/1 is down, line protocol is down (err-disabled)
  Hardware is Gigabit Ethernet, address is 0011.2233.4455 (bia 0011.2233.4455)
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Auto-duplex, Auto-speed, 1000BaseTX/FX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts (0 multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out

SwitchA# show errdisable detect
ErrDisable Reason    Detection Status
------------------  -----------------
udld                Enabled
bpduguard           Enabled
security-violation  Enabled

SwitchA# show interfaces gigabitethernet 0/1 status
Port      Name   Status       Vlan    Duplex  Speed  Type
Gi0/1            err-disabled 1       auto    auto   10/100/1000BaseTX

A network technician connects a new Cisco switch to an existing access switch using a Category 5e copper patch cable. The link fails to come up, and the interface status shows 'err-disabled'. The technician checks the interface diagnostics and the running configuration. What action should the technician take to resolve the problem?

Question 1hardmultiple choice
Study the full ACL explanation →

Exhibit

SwitchA# show interfaces gigabitethernet 0/1
GigabitEthernet0/1 is down, line protocol is down (err-disabled)
  Hardware is Gigabit Ethernet, address is 0011.2233.4455 (bia 0011.2233.4455)
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Auto-duplex, Auto-speed, 1000BaseTX/FX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts (0 multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out

SwitchA# show errdisable detect
ErrDisable Reason    Detection Status
------------------  -----------------
udld                Enabled
bpduguard           Enabled
security-violation  Enabled

SwitchA# show interfaces gigabitethernet 0/1 status
Port      Name   Status       Vlan    Duplex  Speed  Type
Gi0/1            err-disabled 1       auto    auto   10/100/1000BaseTX

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Configure the interface as a trunk port and disable spanning-tree BPDU guard.

The most likely reason for the err-disabled state is a spanning-tree BPDU guard violation on the access switch's port configured with PortFast. When another switch is connected, it sends BPDUs, triggering BPDU guard to error-disable the port. Configuring the interface as a trunk port and disabling BPDU guard (option B) resolves the issue by allowing BPDUs without triggering the protection. Option A is unnecessary because Category 5e supports Gigabit Ethernet. Option C is irrelevant since the problem is not distance-related. Option D is risky because auto-negotiation is preferred and manual settings can cause mismatches.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✗

    Replace the Category 5e cable with a Category 6 cable to support Gigabit Ethernet.

    Why it's wrong here

    Category 5e cable is fully capable of supporting 1000BASE-T (Gigabit Ethernet) up to 100 meters, so a cable upgrade is not necessary.

  • ✓

    Configure the interface as a trunk port and disable spanning-tree BPDU guard.

    Why this is correct

    The port is in err-disabled because bpduguard is enabled. Since this is a connection between two switches, the port should be configured as a trunk (or at least not as an access port with portfast) and bpduguard should be disabled to prevent the errdisable state.

    Related concept

    Read the scenario before looking for a memorised answer.

  • ✗

    Replace the copper SFP with a fiber SFP to increase the distance.

    Why it's wrong here

    The interface diagnostics show the port type is 10/100/1000BaseTX (copper RJ-45), not an SFP slot. The problem is not related to distance or transceiver type.

  • ✗

    Manually set the speed and duplex to 1000 Mbps and full duplex on both switches.

    Why it's wrong here

    While speed/duplex mismatch can cause interface issues, the err-disabled state with bpduguard enabled indicates a BPDU guard violation, not a mismatch. The interface shows auto-negotiation is enabled.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.

✓Configure the interface as a trunk port and disable spanning-tree BPDU guard.Correct answer▾

Why this is correct

The port is in err-disabled because bpduguard is enabled. Since this is a connection between two switches, the port should be configured as a trunk (or at least not as an access port with portfast) and bpduguard should be disabled to prevent the errdisable state.

✗Replace the Category 5e cable with a Category 6 cable to support Gigabit Ethernet.Wrong answer — click to see why▾

Why this is wrong here

The symptom is err-disabled, not a speed or duplex mismatch; cable type is not the issue.

✗Replace the copper SFP with a fiber SFP to increase the distance.Wrong answer — click to see why▾

Why this is wrong here

The port is a built-in copper port, not an SFP-based interface; distance is not the issue.

✗Manually set the speed and duplex to 1000 Mbps and full duplex on both switches.Wrong answer — click to see why▾

Why this is wrong here

The err-disabled state is due to BPDU guard, not speed/duplex mismatch; manual settings would not fix the root cause.

Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that err-disabled is always caused by speed/duplex mismatches or cable issues, but the trap here is that BPDU guard on a PortFast access port is a frequent and specific cause when connecting another switch.

Trap categories for this question

  • Command / output trap

    The interface diagnostics show the port type is 10/100/1000BaseTX (copper RJ-45), not an SFP slot. The problem is not related to distance or transceiver type.

Detailed technical explanation

How to think about this question

BPDU guard is a Cisco feature that, when enabled on a PortFast-enabled port, places the interface into err-disabled state upon receiving any BPDU, preventing potential bridging loops from unauthorized switches. The err-disabled state can be cleared by administrative intervention (e.g., 'shutdown' followed by 'no shutdown') or by configuring 'errdisable recovery cause bpduguard'. In real-world scenarios, connecting an unmanaged switch to a PortFast access port is a common trigger, and the fix involves either disabling BPDU guard or configuring the port as a trunk if trunking is required.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 200-301 question test?

Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Configure the interface as a trunk port and disable spanning-tree BPDU guard. — The most likely reason for the err-disabled state is a spanning-tree BPDU guard violation on the access switch's port configured with PortFast. When another switch is connected, it sends BPDUs, triggering BPDU guard to error-disable the port. Configuring the interface as a trunk port and disabling BPDU guard (option B) resolves the issue by allowing BPDUs without triggering the protection. Option A is unnecessary because Category 5e supports Gigabit Ethernet. Option C is irrelevant since the problem is not distance-related. Option D is risky because auto-negotiation is preferred and manual settings can cause mismatches.

What should I do if I get this 200-301 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 11, 2026

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