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Network Infrastructure and Connectivity →hardTroubleshootingObjective-mapped

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
G0/0192.168.1.1/30linkG0/1192.168.1.5/30G0/1192.168.1.6/30linklinkR2R1Switch1Hosts in VLAN10

You are connected to R1. The network administrator reports that hosts on VLAN 10 cannot communicate with the server attached to R2's GigabitEthernet0/1 interface. Troubleshoot and resolve the issue. Identify the root cause and apply the necessary fix on R1.

Question 1hardTroubleshooting
Open the full VLAN trunking answer →

Exhibit

R1# show interfaces GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
  Hardware is Gigabit Ethernet, address is aaaa.bbbb.cccc (bia aaaa.bbbb.cccc)
  Internet address is 192.168.1.1/30
  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)
  Full-duplex, 1000Mb/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 00:00:05, 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
     12345 packets input, 1234567 bytes
     Received 123 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     1500 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     12345 packets output, 1234567 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

R1# show interfaces GigabitEthernet0/1
GigabitEthernet0/1 is up, line protocol is down
  Hardware is Gigabit Ethernet, address is aaaa.bbbb.cccd (bia aaaa.bbbb.cccd)
  Internet address is 192.168.1.5/30
  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, media type is RJ45
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:05, 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
     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

R1# show running-config interface GigabitEthernet0/0
Building configuration...

Current configuration : 100 bytes
!
interface GigabitEthernet0/0
 no shutdown
 ip address 192.168.1.1 255.255.255.252
 duplex full
 speed 1000
end

R1# show running-config interface GigabitEthernet0/1
Building configuration...

Current configuration : 75 bytes
!
interface GigabitEthernet0/1
 no shutdown
 ip address 192.168.1.5 255.255.255.252
end

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 'no duplex' and 'no speed' under interface GigabitEthernet0/0 to enable auto-negotiation.

The issue is a duplex mismatch on GigabitEthernet0/0. R1 is configured with 'duplex full' and 'speed 1000', but the connected switch port is likely set to auto-negotiate or is set to half-duplex. This causes high input errors (1500) and degraded performance. The fix is to set R1's G0/0 to auto-negotiate both speed and duplex, matching the switch's configuration. Enter interface configuration mode for G0/0, issue 'no duplex' and 'no speed' to revert to auto, then clear the interface counters with 'clear counters gigabitethernet0/0'.

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.

  • ✓

    Configure 'no duplex' and 'no speed' under interface GigabitEthernet0/0 to enable auto-negotiation.

    Why this is correct

    This is correct because the issue is a duplex mismatch on GigabitEthernet0/0. R1 is statically set to full duplex and 1000 Mbps, but the connected switch port likely uses auto-negotiation or half-duplex, causing input errors. Reverting to auto-negotiation with 'no duplex' and 'no speed' allows both sides to negotiate the best settings, resolving the mismatch.

    Related concept

    Authentication checks who the user is.

  • ✗

    Change the duplex setting on GigabitEthernet0/0 to half-duplex using 'duplex half'.

    Why it's wrong here

    This is incorrect because forcing half-duplex on R1's GigabitEthernet0/0 would likely cause a mismatch if the switch is set to full duplex or auto-negotiation, worsening the problem. The correct approach is to enable auto-negotiation on both sides.

  • ✗

    Apply 'speed 100' and 'duplex full' on GigabitEthernet0/0 to match a common switch configuration.

    Why it's wrong here

    This is incorrect because the interface is GigabitEthernet, which typically requires 1000 Mbps. Forcing 100 Mbps and full duplex may not be supported or could cause a speed mismatch. Additionally, the root cause is duplex mismatch, not speed.

  • ✗

    Clear the interface counters on GigabitEthernet0/0 with 'clear counters gigabitethernet0/0' without changing any configuration.

    Why it's wrong here

    This is incorrect because clearing counters only resets statistics; it does not fix the underlying duplex mismatch. The input errors will continue to accumulate after clearing.

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 'no duplex' and 'no speed' under interface GigabitEthernet0/0 to enable auto-negotiation.Correct answer▾

Why this is correct

This is correct because the issue is a duplex mismatch on GigabitEthernet0/0. R1 is statically set to full duplex and 1000 Mbps, but the connected switch port likely uses auto-negotiation or half-duplex, causing input errors. Reverting to auto-negotiation with 'no duplex' and 'no speed' allows both sides to negotiate the best settings, resolving the mismatch.

✗Change the duplex setting on GigabitEthernet0/0 to half-duplex using 'duplex half'.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that manually setting half-duplex does not resolve a mismatch; it may create a new mismatch or degrade performance further.

Why candidates choose this

Candidates might think that since the switch is half-duplex, setting the router to half-duplex will match, but they overlook that the switch may be auto-negotiating or that the router's current full-duplex setting is the problem.

✗Apply 'speed 100' and 'duplex full' on GigabitEthernet0/0 to match a common switch configuration.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that GigabitEthernet interfaces usually operate at 1000 Mbps; setting speed to 100 may cause the interface to not come up or to underperform.

Why candidates choose this

Candidates might think that lowering the speed to 100 Mbps and setting full duplex is a safe fallback, but this ignores the interface's capabilities and the actual issue of duplex mismatch.

✗Clear the interface counters on GigabitEthernet0/0 with 'clear counters gigabitethernet0/0' without changing any configuration.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that clearing counters is a diagnostic step, not a fix. The root cause (duplex mismatch) remains unaddressed.

Why candidates choose this

Candidates might think that clearing counters resolves the issue because it temporarily removes the error count, but they fail to recognize that the problem persists.

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 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 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: Configure 'no duplex' and 'no speed' under interface GigabitEthernet0/0 to enable auto-negotiation. — The issue is a duplex mismatch on GigabitEthernet0/0. R1 is configured with 'duplex full' and 'speed 1000', but the connected switch port is likely set to auto-negotiate or is set to half-duplex. This causes high input errors (1500) and degraded performance. The fix is to set R1's G0/0 to auto-negotiate both speed and duplex, matching the switch's configuration. Enter interface configuration mode for G0/0, issue 'no duplex' and 'no speed' to revert to auto, then clear the interface counters with 'clear counters gigabitethernet0/0'.

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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