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CCNA Practice Question: A network administrator is troubleshooting a…

This 200-301 practice question tests your understanding of 200-301 exam topics. 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

C:\) ipconfig

Ethernet adapter Local Area Connection:
   Connection-specific DNS Suffix  . :
   IPv4 Address. . . . . . . . . . . : 169.254.10.15
   Subnet Mask . . . . . . . . . . . : 255.255.0.0
   Default Gateway . . . . . . . . . :

Switch# show interfaces gigabitethernet 0/1 status
Port      Name   Status       Vlan   Duplex  Speed Type
Gi0/1            connected    100    a-full  a-100 10/100/1000BaseTX

Switch# show running-config interface gigabitethernet 0/1
Building configuration...

Current configuration : 100 bytes
!
interface GigabitEthernet0/1
 description Client Access Port
 switchport mode access
 switchport access vlan 100
 spanning-tree portfast
end

A network administrator is troubleshooting a Windows 10 client that cannot reach the internet. The client is connected to a Cisco switch port configured as an access port in VLAN 100. The administrator runs ipconfig on the client and sees an IP address of 169.254.10.15 with a subnet mask of 255.255.0.0. The switch port shows status up/up. What is the most likely cause of the issue?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

  • Clue: "most likely"

    Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1hardmultiple choice
Full question →

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

✓

The switch is not configured with an ip helper-address on the VLAN 100 SVI to forward DHCP broadcasts to the DHCP server.

The client has an Automatic Private IP Addressing (APIPA) address (169.254.x.x), which indicates it failed to obtain an IP address from a DHCP server. The switch port is correctly configured as an access port in VLAN 100 and is up/up, so the issue is not at Layer 1 or Layer 2. The most common reason for DHCP failure in this scenario is that the DHCP server is not reachable from VLAN 100—either the DHCP server is in a different VLAN and no DHCP relay (ip helper-address) is configured on the switch SVI for VLAN 100, or the DHCP server itself is down. Option B correctly identifies the missing DHCP relay. Options A, C, and D are incorrect because the port is not in err-disabled, the client is not in the wrong VLAN (the switchport configuration matches), and there is no duplex mismatch (the switch reports a-full).

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.

  • ✗

    The switch port is in err-disabled state due to a spanning-tree loop.

    Why it's wrong here

    The output shows the port is 'connected', not err-disabled, so this is not the issue.

  • ✓

    The switch is not configured with an ip helper-address on the VLAN 100 SVI to forward DHCP broadcasts to the DHCP server.

    Why this is correct

    Without an ip helper-address, DHCP broadcasts from the client in VLAN 100 are not forwarded to the DHCP server, which is likely in a different VLAN.

    Clue confirmation

    The clue word "most likely" in the question point toward this answer.

    Related concept

    Access ports place end devices into a single VLAN.

  • ✗

    The client is in the wrong VLAN; the switch should be configured with VLAN 200.

    Why it's wrong here

    The switchport is configured for VLAN 100, and there is no evidence that the client should be in a different VLAN.

  • ✗

    There is a duplex mismatch between the client and the switch.

    Why it's wrong here

    The switch reports 'a-full' (auto-negotiated full duplex), indicating no duplex mismatch.

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.

✓The switch is not configured with an ip helper-address on the VLAN 100 SVI to forward DHCP broadcasts to the DHCP server.Correct answer▾

Why this is correct

Without an ip helper-address, DHCP broadcasts from the client in VLAN 100 are not forwarded to the DHCP server, which is likely in a different VLAN.

✗The switch port is in err-disabled state due to a spanning-tree loop.Wrong answer — click to see why▾

Why this is wrong here

The port status is 'connected', not err-disabled.

✗The client is in the wrong VLAN; the switch should be configured with VLAN 200.Wrong answer — click to see why▾

Why this is wrong here

No information suggests the client should be in VLAN 200; the configuration matches the intended VLAN.

✗There is a duplex mismatch between the client and the switch.Wrong answer — click to see why▾

Why this is wrong here

Duplex mismatch would typically cause errors or speed/duplex issues, but the switch shows a-full, so this is not the problem.

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 output shows the port is 'connected', not err-disabled, so this is not the issue.

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?

Access ports place end devices into a single VLAN.

What is the correct answer to this question?

The correct answer is: The switch is not configured with an ip helper-address on the VLAN 100 SVI to forward DHCP broadcasts to the DHCP server. — The client has an Automatic Private IP Addressing (APIPA) address (169.254.x.x), which indicates it failed to obtain an IP address from a DHCP server. The switch port is correctly configured as an access port in VLAN 100 and is up/up, so the issue is not at Layer 1 or Layer 2. The most common reason for DHCP failure in this scenario is that the DHCP server is not reachable from VLAN 100—either the DHCP server is in a different VLAN and no DHCP relay (ip helper-address) is configured on the switch SVI for VLAN 100, or the DHCP server itself is down. Option B correctly identifies the missing DHCP relay. Options A, C, and D are incorrect because the port is not in err-disabled, the client is not in the wrong VLAN (the switchport configuration matches), and there is no duplex mismatch (the switch reports a-full).

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.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Access ports place end devices into a single VLAN.

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