CCNA Network Infrastructure and Connectivity Practice Question
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 10/100/1000BaseTXA 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?
⚠ Common exam trap
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.
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.
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 rated for 1000BASE-T (Gigabit Ethernet) over distances up to 100 meters, so the cable is not the bottleneck. The real cause of the outage is that the port entered err-disabled because BPDU guard detected a spanning-tree bridge protocol data unit from the connected switch. Replacing the cable would not clear the err-disabled state nor prevent the BPDU guard violation that triggered it.
- ✓
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.
- ✗
Replace the copper SFP with a fiber SFP to increase the distance.
Why it's wrong here
The interface is a 10/100/1000BaseTX copper RJ-45 port, not an SFP transceiver slot, so a fiber SFP cannot be inserted into this port anyway. The fault is not about distance or media type; it is an err-disabled port caused by BPDU guard shutting down the port when it received a BPDU on a PortFast-enabled access port. Changing to fiber would neither reset the err-disabled interface nor address the spanning-tree misconfiguration.
- ✗
Manually set the speed and duplex to 1000 Mbps and full duplex on both switches.
Why it's wrong here
While a speed/duplex mismatch can cause collisions and excessive CRC errors, the show output indicates auto-negotiation is enabled and the interface state is err-disabled, not down/down from a mismatch. BPDU guard is the specific feature that places the port into err-disabled state after receiving a BPDU, and manual speed/duplex settings would not recover the port or stop the BPDU guard violation. To restore operation, you must either disable bpduguard or configure the port as a trunk and then clear the err-disabled state.
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?”
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Related to this question
Learn chapter
Network Topology Types
Key term
CAN
A CAN (Controller Area Network) is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other without a host computer.
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.