Question 826 of 2,015

NAT and DHCP →easyMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the router’s interface is not configured with an IP address in the 192.168.1.0/24 subnet. Even though the DHCP pool correctly specifies 192.168.1.1 as the default gateway, the router’s own interface must belong to that same subnet and be in an up/up state for clients to reach it. When the interface lacks the proper IP or is administratively down, clients receive a valid lease but cannot forward traffic to the gateway, resulting in a “DHCP server default gateway unreachable” scenario. On the ENCOR 350-401 exam, this question tests your understanding that DHCP server configuration and interface addressing are separate tasks—a common trap is assuming the default-router option alone ensures connectivity. The key is to verify the interface’s IP and status before troubleshooting other issues. Memory tip: “Lease doesn’t mean reachable—check the interface’s address and state.”

350-401 NAT and DHCP Practice Question

This 350-401 practice question tests your understanding of nat and dhcp. 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 configuring a Cisco router to act as a DHCP server for a branch office. The engineer creates a DHCP pool for the 192.168.1.0/24 subnet and configures the default-router, dns-server, and domain-name options. However, clients are able to obtain IP addresses but cannot ping the default gateway. The engineer verifies that the router's interface IP is 192.168.1.1. 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.

Question 1easymultiple choice

Read the full DHCP explanation →

A
The router's interface is not configured with an IP address in the 192.168.1.0/24 subnet.
Correct because if the router interface is not in the same subnet, the clients will have a default gateway that is unreachable.
B
The DHCP pool is missing the lease command.
Why wrong: Incorrect because the lease command is optional; without it, a default lease is used, and clients can still ping the gateway.
C
The router's interface is administratively down.
Why wrong: Incorrect because if the interface were down, the DHCP server would not be able to assign addresses from that subnet (the pool would be inactive).
D
The ip dhcp excluded-address command is blocking the default gateway IP.
Why wrong: Incorrect because the excluded-address command prevents the DHCP server from assigning that IP to a client, but the router still owns it.

Full breakdown with real-world context →

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's interface is not configured with an IP address in the 192.168.1.0/24 subnet.

The DHCP server assigns the default gateway, but if the router's interface is not in the same subnet as the pool or if the interface is down, clients cannot reach it.

Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

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 router's interface is not configured with an IP address in the 192.168.1.0/24 subnet.
Why this is correct
Correct because if the router interface is not in the same subnet, the clients will have a default gateway that is unreachable.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
The DHCP pool is missing the lease command.
Why it's wrong here
Incorrect because the lease command is optional; without it, a default lease is used, and clients can still ping the gateway.
✗
The router's interface is administratively down.
Why it's wrong here
Incorrect because if the interface were down, the DHCP server would not be able to assign addresses from that subnet (the pool would be inactive).
✗
The ip dhcp excluded-address command is blocking the default gateway IP.
Why it's wrong here
Incorrect because the excluded-address command prevents the DHCP server from assigning that IP to a client, but the router still owns it.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.

Trap categories for this question

Command / output trap
Incorrect because the lease command is optional; without it, a default lease is used, and clients can still ping the gateway.

Detailed technical explanation

How to think about this question

Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

Key takeaway

Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

Real-world example

How this comes up in practice

A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.

What to study next

Got this wrong? Here's your next step.

Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 350-401 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this 350-401 question test?

NAT and DHCP — This question tests NAT and DHCP — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The router's interface is not configured with an IP address in the 192.168.1.0/24 subnet. — The DHCP server assigns the default gateway, but if the router's interface is not in the same subnet as the pool or if the interface is down, clients cannot reach it.

What should I do if I get this 350-401 question wrong?

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?

CIDR notation defines the prefix length.

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