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Switching and Network Access →hardTroubleshootingObjective-mapped

CCNA Switching and Network Access Practice Question

This 200-301 practice question tests your understanding of switching and network access. 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.

Network Topology
Fa0/1Fa0/2Access SwitchSiR1Another Switch

You are connected to R1, a multilayer switch running Rapid PVST+. The current root bridge for VLAN 10 has priority 24586 and for VLAN 20 has priority 24676. Configure R1 so that it becomes the root bridge for VLAN 10 and VLAN 20. Then enable PortFast and BPDU Guard on interface FastEthernet0/1, which connects to an access switch. Finally, diagnose why interface FastEthernet0/2 has entered an err-disabled state and recover it.

Question 1hardTroubleshooting
Open the full VLAN trunking answer →

Exhibit

R1# show spanning-tree

VLAN0001
  Spanning tree enabled protocol rstp
  Root ID    Priority    32769
             Address     0011.2233.4401
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0011.2233.4401
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1               Desg FWD 19        128.1    P2p
Fa0/2               Desg FWD 19        128.2    P2p

VLAN0010
  Spanning tree enabled protocol rstp
  Root ID    Priority    24586
             Address     0011.2233.4402
             Cost        19
             Port        1 (FastEthernet0/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32778  (priority 32768 sys-id-ext 10)
             Address     0011.2233.4401
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1               Root FWD 19        128.1    P2p
Fa0/2               Altn BLK 19        128.2    P2p

VLAN0020
  Spanning tree enabled protocol rstp
  Root ID    Priority    24676
             Address     0011.2233.4402
             Cost        19
             Port        1 (FastEthernet0/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32788  (priority 32768 sys-id-ext 20)
             Address     0011.2233.4401
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1               Root FWD 19        128.1    P2p
Fa0/2               Altn BLK 19        128.2    P2p

R1# show interfaces fastEthernet 0/2
FastEthernet0/2 is down, line protocol is down (err-disabled)
  Hardware is Fast Ethernet, address is 0011.2233.4402 (bia 0011.2233.4402)
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Auto-duplex, 100Mb/s
  input flow-control is off, output flow-control is off
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:08, output 00:00:05, 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
     Received 0 broadcasts (0 IP multicasts)
     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

R1# show running-config | section interface FastEthernet0/2
interface FastEthernet0/2
 switchport mode access
 switchport access vlan 10
 spanning-tree bpduguard enable

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 spanning-tree vlan 10,20 priority 4096; on Fa0/1: spanning-tree portfast and spanning-tree bpduguard enable; on Fa0/2: shutdown then no shutdown.

To become the root bridge, R1’s priority must be lower than the current root’s priority. Setting the priority to 4096 (or any value lower than 24586/24676) accomplishes this. Option A correctly uses `spanning-tree vlan 10,20 priority 4096` (though the actual command per VLAN is `spanning-tree vlan 10 priority 4096` and `spanning-tree vlan 20 priority 4096`). It also enables PortFast and BPDU Guard on Fa0/1 to prevent BPDU reception on an edge port, and recovers the err-disabled Fa0/2 by cycling `shutdown` then `no shutdown`. Options B and C fail because they do not enable BPDU Guard, leaving the interface vulnerable. Option D fails because it only shuts down Fa0/2 without the `no shutdown` command, so the interface remains administratively down.

Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.

Answer analysis

Option-by-option breakdown

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

  • ✓

    Configure spanning-tree vlan 10,20 priority 4096; on Fa0/1: spanning-tree portfast and spanning-tree bpduguard enable; on Fa0/2: shutdown then no shutdown.

    Why this is correct

    Setting the priority to 4096 makes R1 the root for VLANs 10 and 20 because it is lower than the current root priorities (24586 and 24676). PortFast and BPDU Guard are correctly configured on Fa0/1. The err-disabled state on Fa0/2 is due to BPDU Guard; recovery requires a shutdown/no shutdown cycle.

    Related concept

    Access ports place end devices into a single VLAN.

  • ✗

    Configure spanning-tree vlan 10,20 root primary; on Fa0/1: spanning-tree portfast; on Fa0/2: no shutdown.

    Why it's wrong here

    The 'root primary' command sets priority to 24576, which is not lower than the current root priority for VLAN 10 (24586) and VLAN 20 (24676), so R1 would not become root. Also, BPDU Guard is missing on Fa0/1, and simply 'no shutdown' on Fa0/2 does not recover from err-disable; the interface must be shut first.

  • ✗

    Configure spanning-tree vlan 10,20 priority 8192; on Fa0/1: spanning-tree portfast; on Fa0/2: no shutdown.

    Why it's wrong here

    Priority 8192 is lower than the current root priorities (24586 and 24676), so R1 would become root. However, BPDU Guard is missing on Fa0/1, and the recovery command for Fa0/2 is incomplete; you must first shut down the interface before no shutdown.

  • ✗

    Configure spanning-tree vlan 10,20 priority 4096; on Fa0/1: spanning-tree portfast and spanning-tree bpduguard enable; on Fa0/2: shutdown.

    Why it's wrong here

    The priority and PortFast/BPDU Guard configurations are correct. However, the recovery command for Fa0/2 is incomplete; after shutdown, you must also issue 'no shutdown' to bring the interface back up.

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 spanning-tree vlan 10,20 priority 4096; on Fa0/1: spanning-tree portfast and spanning-tree bpduguard enable; on Fa0/2: shutdown then no shutdown.Correct answer▾

Why this is correct

Setting the priority to 4096 makes R1 the root for VLANs 10 and 20 because it is lower than the current root priorities (24586 and 24676). PortFast and BPDU Guard are correctly configured on Fa0/1. The err-disabled state on Fa0/2 is due to BPDU Guard; recovery requires a shutdown/no shutdown cycle.

✗Configure spanning-tree vlan 10,20 root primary; on Fa0/1: spanning-tree portfast; on Fa0/2: no shutdown.Wrong answer — click to see why▾

Why this is wrong here

The 'root primary' command sets priority to 24576, which is higher than the current root priority for VLAN 10 (24586) and VLAN 20 (24676) — actually 24576 is lower than 24586 and 24676, so it would become root. Wait, check: 24576 < 24586, so it would become root. But the command 'root primary' sets priority to 24576 only if the current root priority is above 24576; if the current root priority is 24586, it sets to 24576, which is lower, so R1 would become root. However, the question states the current root has priority 24586 and 24676, so 'root primary' would set to 24576, which is lower than 24586 but not lower than 24676? Actually 24576 < 24676, so it would become root for both. But the correct answer uses 4096, which is even lower. The key is that 'root primary' might not guarantee becoming root if another switch has a lower priority. Also, BPDU Guard is missing, and recovery requires shutdown first.

Why candidates choose this

Candidates often think 'root primary' is a shortcut to become root, but it only sets priority to 24576, which may not be low enough if another switch has a lower priority. Also, they may forget BPDU Guard and proper err-disable recovery.

✗Configure spanning-tree vlan 10,20 priority 8192; on Fa0/1: spanning-tree portfast; on Fa0/2: no shutdown.Wrong answer — click to see why▾

Why this is wrong here

BPDU Guard is not configured on Fa0/1, leaving the port vulnerable to BPDU attacks. Also, the err-disabled recovery requires a shutdown command before no shutdown.

Why candidates choose this

Candidates may think PortFast alone is sufficient for edge ports, but BPDU Guard is also needed to prevent loops. They may also think 'no shutdown' alone can recover an err-disabled interface.

✗Configure spanning-tree vlan 10,20 priority 4096; on Fa0/1: spanning-tree portfast and spanning-tree bpduguard enable; on Fa0/2: shutdown.Wrong answer — click to see why▾

Why this is wrong here

Simply shutting down the interface does not recover it from err-disable; you must also re-enable it with 'no shutdown'.

Why candidates choose this

Candidates may think that shutting down the interface is enough to clear the err-disable state, but the interface remains disabled until a 'no shutdown' is issued.

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: an active trunk can still block the VLAN you need

A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.

Trap categories for this question

  • Command / output trap

    The 'root primary' command sets priority to 24576, which is not lower than the current root priority for VLAN 10 (24586) and VLAN 20 (24676), so R1 would not become root. Also, BPDU Guard is missing on Fa0/1, and simply 'no shutdown' on Fa0/2 does not recover from err-disable; the interface must be shut first.

Detailed technical explanation

How to think about this question

VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.

KKey Concepts to Remember

  • Access ports place end devices into a single VLAN.
  • Trunk ports carry multiple VLANs between switches.
  • Allowed VLAN lists decide which VLANs can cross a trunk.
  • Native VLAN mismatch can create confusing symptoms.

TExam Day Tips

  • Use show vlan brief to verify access VLANs.
  • Use show interfaces trunk to verify trunk state and allowed VLANs.
  • Do not treat every same-VLAN issue as a routing problem.

Key takeaway

A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.

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.

Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.

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FAQ

Questions learners often ask

What does this 200-301 question test?

Switching and Network Access — This question tests Switching and Network Access — Access ports place end devices into a single VLAN..

What is the correct answer to this question?

The correct answer is: Configure spanning-tree vlan 10,20 priority 4096; on Fa0/1: spanning-tree portfast and spanning-tree bpduguard enable; on Fa0/2: shutdown then no shutdown. — To become the root bridge, R1’s priority must be lower than the current root’s priority. Setting the priority to 4096 (or any value lower than 24586/24676) accomplishes this. Option A correctly uses `spanning-tree vlan 10,20 priority 4096` (though the actual command per VLAN is `spanning-tree vlan 10 priority 4096` and `spanning-tree vlan 20 priority 4096`). It also enables PortFast and BPDU Guard on Fa0/1 to prevent BPDU reception on an edge port, and recovers the err-disabled Fa0/2 by cycling `shutdown` then `no shutdown`. Options B and C fail because they do not enable BPDU Guard, leaving the interface vulnerable. Option D fails because it only shuts down Fa0/2 without the `no shutdown` command, so the interface remains administratively down.

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

Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.

What is the key concept behind this question?

Access ports place end devices into a single VLAN.

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Last reviewed: Jun 6, 2026

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