CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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
R1#show running-config | section dhcp
ip dhcp excluded-address 192.168.100.1 192.168.100.10
ip dhcp excluded-address 192.168.100.254
!
ip dhcp pool POOL_100
network 192.168.100.0 255.255.255.0
default-router 192.168.100.254
dns-server 8.8.8.8
!
interface GigabitEthernet0/0
ip address 192.168.100.1 255.255.255.0
no shut
!
interface GigabitEthernet0/1
ip address 10.1.1.1 255.255.255.0
ip helper-address 192.168.100.254
no shut
You are connected to R1. Configure R1 as a DHCP server for the 192.168.100.0/24 subnet, reserving the first 10 addresses and the address 192.168.100.254 for static assignments, with default gateway 192.168.100.1 and DNS server 8.8.8.8. Then, on the same router, enable DHCP relay for the 10.1.1.0/24 subnet by configuring the helper address pointing to the DHCP server at 192.168.100.1. Finally, verify that the DHCP pool is correctly configured and that the helper address is set.
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
R1#show running-config | section dhcp
ip dhcp excluded-address 192.168.100.1 192.168.100.10
ip dhcp excluded-address 192.168.100.254
!
ip dhcp pool POOL_100
network 192.168.100.0 255.255.255.0
default-router 192.168.100.254
dns-server 8.8.8.8
!
interface GigabitEthernet0/0
ip address 192.168.100.1 255.255.255.0
no shut
!
interface GigabitEthernet0/1
ip address 10.1.1.1 255.255.255.0
ip helper-address 192.168.100.254
no shut
A
The default-router is incorrectly set to 192.168.100.254 instead of 192.168.100.1, and the ip helper-address on G0/1 points to 192.168.100.254 instead of 192.168.100.1.
This is correct because the default-router should be the gateway address 192.168.100.1, not the excluded address 192.168.100.254. Also, the helper-address must point to the DHCP server's IP, which is the router's own interface IP 192.168.100.1, not the excluded address.
B
The default-router is correctly set to 192.168.100.1, but the ip helper-address on G0/1 points to 192.168.100.254 instead of 192.168.100.1.
Why wrong: This is incorrect because while the default-router is correct, the helper-address is wrong. The helper-address must point to the DHCP server's IP, which is 192.168.100.1, not 192.168.100.254.
C
The default-router is incorrectly set to 192.168.100.254 instead of 192.168.100.1, but the ip helper-address on G0/1 correctly points to 192.168.100.1.
Why wrong: This is incorrect because the default-router is wrong; it should be 192.168.100.1, not 192.168.100.254. The helper-address is correct in this option.
D
Both the default-router and the ip helper-address are correctly configured as 192.168.100.1.
Why wrong: This is incorrect because the configuration described in the question has errors; the default-router and helper-address are both set to 192.168.100.254 in the actual scenario, not 192.168.100.1.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The default-router is incorrectly set to 192.168.100.254 instead of 192.168.100.1, and the ip helper-address on G0/1 points to 192.168.100.254 instead of 192.168.100.1.
The configuration has two critical errors. First, the default-router in the DHCP pool is incorrectly set to 192.168.100.254, which is an excluded address meant for static assignment, not the actual gateway (192.168.100.1). Second, the ip helper-address on G0/1 points to 192.168.100.254 (the wrong address) instead of the DHCP server's own interface IP 192.168.100.1. To fix, change the default-router to 192.168.100.1 and update the helper-address to 192.168.100.1.
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 default-router is incorrectly set to 192.168.100.254 instead of 192.168.100.1, and the ip helper-address on G0/1 points to 192.168.100.254 instead of 192.168.100.1.
Why this is correct
This is correct because the default-router should be the gateway address 192.168.100.1, not the excluded address 192.168.100.254. Also, the helper-address must point to the DHCP server's IP, which is the router's own interface IP 192.168.100.1, not the excluded address.
Clue confirmation
The clue word "first" in the question point toward this answer.
The default-router is correctly set to 192.168.100.1, but the ip helper-address on G0/1 points to 192.168.100.254 instead of 192.168.100.1.
Why it's wrong here
This is incorrect because while the default-router is correct, the helper-address is wrong. The helper-address must point to the DHCP server's IP, which is 192.168.100.1, not 192.168.100.254.
✗
The default-router is incorrectly set to 192.168.100.254 instead of 192.168.100.1, but the ip helper-address on G0/1 correctly points to 192.168.100.1.
Why it's wrong here
This is incorrect because the default-router is wrong; it should be 192.168.100.1, not 192.168.100.254. The helper-address is correct in this option.
✗
Both the default-router and the ip helper-address are correctly configured as 192.168.100.1.
Why it's wrong here
This is incorrect because the configuration described in the question has errors; the default-router and helper-address are both set to 192.168.100.254 in the actual scenario, not 192.168.100.1.
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 default-router is incorrectly set to 192.168.100.254 instead of 192.168.100.1, and the ip helper-address on G0/1 points to 192.168.100.254 instead of 192.168.100.1.Correct answer▾
Why this is correct
This is correct because the default-router should be the gateway address 192.168.100.1, not the excluded address 192.168.100.254. Also, the helper-address must point to the DHCP server's IP, which is the router's own interface IP 192.168.100.1, not the excluded address.
✗The default-router is correctly set to 192.168.100.1, but the ip helper-address on G0/1 points to 192.168.100.254 instead of 192.168.100.1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the helper-address should be the DHCP server's IP, not an excluded address.
Why candidates choose this
Candidates might think the helper-address should point to the excluded address reserved for the server, but the server is the router itself, so it should point to the router's interface IP.
✗The default-router is incorrectly set to 192.168.100.254 instead of 192.168.100.1, but the ip helper-address on G0/1 correctly points to 192.168.100.1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the default-router must be the gateway address, not an excluded address.
Why candidates choose this
Candidates might confuse the excluded address with the gateway, thinking the gateway should be the last usable address, but the gateway is explicitly given as 192.168.100.1.
✗Both the default-router and the ip helper-address are correctly configured as 192.168.100.1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the question states the configuration uses 192.168.100.254 for both, so this option does not match the given scenario.
Why candidates choose this
Candidates might think this is the correct configuration, but the question explicitly says the configuration has errors, so this option is not the answer.
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: 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
Scenario analysis trap
This is incorrect because the configuration described in the question has errors; the default-router and helper-address are both set to 192.168.100.254 in the actual scenario, not 192.168.100.1.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
Network Services and Security — This question tests Network Services and Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The default-router is incorrectly set to 192.168.100.254 instead of 192.168.100.1, and the ip helper-address on G0/1 points to 192.168.100.254 instead of 192.168.100.1. — The configuration has two critical errors. First, the default-router in the DHCP pool is incorrectly set to 192.168.100.254, which is an excluded address meant for static assignment, not the actual gateway (192.168.100.1). Second, the ip helper-address on G0/1 points to 192.168.100.254 (the wrong address) instead of the DHCP server's own interface IP 192.168.100.1. To fix, change the default-router to 192.168.100.1 and update the helper-address to 192.168.100.1.
What should I do if I get this 200-301 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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