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Network Infrastructure and Connectivity →hardTroubleshootingObjective-mapped

Quick Answer

The correct answer is to enter interface configuration mode for G0/0 and issue the 'no loopback' command. This resolves the interface loopback condition because the interface status shows '(looped)' in the line status, indicating a Layer 1 loop—often caused by a physical cable loopback or a misconfigured loopback test—where the interface is physically up and line protocol is up, but the loop prevents normal data flow. On the CCNA 200-301 v2 exam, this scenario tests your ability to recognize an interface loop condition from the 'show interfaces' output, where the looped flag is a common trap that leads candidates to mistakenly check cabling or duplex mismatches instead of the loopback test configuration. The key is that 'loopback' is a diagnostic command that must be removed with 'no loopback' to restore stable operation. Memory tip: If you see "looped" but the cable looks fine, think "no loopback" to break the digital loop.

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.

Network Topology
G0/010.0.0.1/30G0/010.0.0.2/30linkR1R2

You are connected to R1. The connection between R1 and R2 is experiencing intermittent failures. Troubleshoot the interface G0/0 on R1 to identify and resolve the issue so that the link becomes stable and operational.

Question 1hardTroubleshooting
Full question →

Exhibit

R1# show interfaces gigabitEthernet 0/0
GigabitEthernet0/0 is up, line protocol is up (looped)
  Hardware is Gigabit Ethernet, address is aabb.cc00.0100 (bia aabb.cc00.0100)
  Internet address is 10.0.0.1/30
  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)
  Full-duplex, 100Mb/s, media type is RJ45
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output 00:00:00, 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 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, 0 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

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

✓

Enter interface configuration mode for G0/0 and issue the 'no loopback' command.

The interface shows '(looped)' in the line status, indicating a layer 1 loop (likely a cable loopback) or a misconfigured loopback test. The interface is physically up and line protocol is up, but the loop condition prevents normal data flow. To fix this, you must remove the loopback test with 'no loopback' on the interface, then verify the interface recovers to 'up, line protocol is up' without the loop indication.

Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.

Answer analysis

Option-by-option breakdown

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

  • ✓

    Enter interface configuration mode for G0/0 and issue the 'no loopback' command.

    Why this is correct

    The interface shows '(looped)' in the line status, indicating a loopback test is enabled. Removing the loopback with 'no loopback' will restore normal operation.

    Related concept

    Authentication checks who the user is.

  • ✗

    Enter interface configuration mode for G0/0 and issue the 'no shutdown' command.

    Why it's wrong here

    The interface is already administratively up (status is 'up'), so 'no shutdown' is not needed. The issue is a loop condition, not an administrative shutdown.

  • ✗

    Enter interface configuration mode for G0/0 and issue the 'speed 100' command to force 100 Mbps.

    Why it's wrong here

    Speed mismatch is not indicated; the interface is up and line protocol is up. Forcing speed could cause a mismatch and worsen the issue.

  • ✗

    Enter interface configuration mode for G0/0 and issue the 'no keepalive' command.

    Why it's wrong here

    Disabling keepalives is not a standard troubleshooting step for a loop condition and could cause the interface to appear up even when the link is down.

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.

✓Enter interface configuration mode for G0/0 and issue the 'no loopback' command.Correct answer▾

Why this is correct

The interface shows '(looped)' in the line status, indicating a loopback test is enabled. Removing the loopback with 'no loopback' will restore normal operation.

✗Enter interface configuration mode for G0/0 and issue the 'no shutdown' command.Wrong answer — click to see why▾

Why this is wrong here

The interface is not administratively down; 'no shutdown' would have no effect on a loop condition.

Why candidates choose this

Candidates often default to 'no shutdown' when troubleshooting interface issues, but here the problem is a loopback test, not a shutdown.

✗Enter interface configuration mode for G0/0 and issue the 'speed 100' command to force 100 Mbps.Wrong answer — click to see why▾

Why this is wrong here

The problem is a loopback test, not a speed/duplex mismatch. Changing speed may cause additional problems.

Why candidates choose this

Candidates may think intermittent failures are due to speed/duplex mismatch, but the '(looped)' indicator points to a loopback test.

✗Enter interface configuration mode for G0/0 and issue the 'no keepalive' command.Wrong answer — click to see why▾

Why this is wrong here

Keepalives are used to detect link failures; disabling them would not resolve a loopback test and could mask real issues.

Why candidates choose this

Some candidates confuse loopback with keepalive issues, but the '(looped)' status specifically indicates a loopback test is active.

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: authentication is not authorization

Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.

Detailed technical explanation

How to think about this question

This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.

KKey Concepts to Remember

  • Authentication checks who the user is.
  • Authorization controls what the user is allowed to do after login.
  • Privilege levels affect access to EXEC and configuration commands.
  • AAA, TACACS+ and RADIUS can separate login success from command access.

TExam Day Tips

  • Do not assume successful login means full administrative access.
  • Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
  • Separate login problems from permission problems before choosing the answer.

Key takeaway

Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.

Real-world example

How this comes up in practice

A practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related 200-301 questions on access control and AAA configuration.

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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 — Authentication checks who the user is..

What is the correct answer to this question?

The correct answer is: Enter interface configuration mode for G0/0 and issue the 'no loopback' command. — The interface shows '(looped)' in the line status, indicating a layer 1 loop (likely a cable loopback) or a misconfigured loopback test. The interface is physically up and line protocol is up, but the loop condition prevents normal data flow. To fix this, you must remove the loopback test with 'no loopback' on the interface, then verify the interface recovers to 'up, line protocol is up' without the loop indication.

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

Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related 200-301 questions on access control and AAA configuration.

What is the key concept behind this question?

Authentication checks who the user is.

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Last reviewed: Jun 6, 2026

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