- A
The DHCP pool has the wrong subnet mask.
Why wrong: Incorrect because the subnet mask affects the client's network prefix, but the default gateway IP is still reachable if it's on the same subnet; the issue is that the gateway itself is unreachable.
- B
The router interface Gi0/0 is administratively down.
Correct because if the interface is down, the router cannot respond to ARP requests or pings from clients, even though DHCP assignments are still possible (the server process runs independently).
- C
The 'ip helper-address' command is interfering with DHCP.
Why wrong: Incorrect because the router is the DHCP server, not a relay; helper-address is not used in this scenario.
- D
The clients have a static ARP entry for the gateway.
Why wrong: Incorrect because static ARP would not cause pings to fail; it would actually help if the ARP entry is correct.
Quick Answer
The answer is that the router interface Gi0/0 is administratively down. When DHCP clients cannot ping the default gateway despite receiving a valid IP address and gateway from the pool, the issue is almost always a Layer 2 or Layer 3 connectivity problem at the router interface itself. Even though the `default-router` command points to 192.168.1.1 and the interface is configured with that same IP, if the interface is shut down, the router will not respond to ARP requests or forward traffic, making the gateway unreachable from the client’s perspective. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to distinguish between DHCP configuration errors and interface state issues—a common trap is to overthink VLAN mismatches or ACLs when the simplest cause is an administratively down interface. Remember the memory tip: “If the gateway is silent, check if the port is silent too.”
300-410 DHCP (IPv4 and IPv6) Practice Question
This 300-410 practice question tests your understanding of dhcp (ipv4 and ipv6). 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.
A network engineer is troubleshooting a DHCPv4 issue where clients on a subnet are getting IP addresses from the correct pool, but they cannot reach the default gateway. The router is configured as a DHCP server with pool 'POOL' that includes 'default-router 192.168.1.1'. The router's interface IP is 192.168.1.1/24. Clients receive the address and default gateway, but pings to 192.168.1.1 fail. What is the most likely cause?
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.
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 router interface Gi0/0 is administratively down.
If the router's interface is up and has the correct IP, but clients cannot ping the gateway, the issue is often that the interface is in a different VLAN or the clients are on a different broadcast domain. However, the most common misconfiguration is that the 'default-router' command points to an IP that is not actually configured on the router's interface, or the interface is down. Given that the symptom is specific to the gateway, the likely cause is that the interface is shut down or has a different IP.
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 DHCP pool has the wrong subnet mask.
Why it's wrong here
Incorrect because the subnet mask affects the client's network prefix, but the default gateway IP is still reachable if it's on the same subnet; the issue is that the gateway itself is unreachable.
- ✓
The router interface Gi0/0 is administratively down.
Why this is correct
Correct because if the interface is down, the router cannot respond to ARP requests or pings from clients, even though DHCP assignments are still possible (the server process runs independently).
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 'ip helper-address' command is interfering with DHCP.
Why it's wrong here
Incorrect because the router is the DHCP server, not a relay; helper-address is not used in this scenario.
- ✗
The clients have a static ARP entry for the gateway.
Why it's wrong here
Incorrect because static ARP would not cause pings to fail; it would actually help if the ARP entry is correct.
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
Scenario analysis trap
Incorrect because the router is the DHCP server, not a relay; helper-address is not used in this scenario.
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 300-410 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 300-410 question test?
DHCP (IPv4 and IPv6) — This question tests DHCP (IPv4 and IPv6) — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The router interface Gi0/0 is administratively down. — If the router's interface is up and has the correct IP, but clients cannot ping the gateway, the issue is often that the interface is in a different VLAN or the clients are on a different broadcast domain. However, the most common misconfiguration is that the 'default-router' command points to an IP that is not actually configured on the router's interface, or the interface is down. Given that the symptom is specific to the gateway, the likely cause is that the interface is shut down or has a different IP.
What should I do if I get this 300-410 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 300-410 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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Last reviewed: Jun 19, 2026
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