- A
ip helper-address 172.16.1.100
This command, when applied to the LAN-facing interface (GigabitEthernet0/1 or similar), converts the DHCP broadcast into a unicast directed to the DHCP server at 172.16.1.100, enabling cross-subnet DHCP.
- B
ip dhcp relay information option
Why wrong: This command enables the insertion of DHCP relay agent information (Option 82), but does not by itself forward broadcasts to a specific server.
- C
ip forward-protocol udp 67
Why wrong: This command enables forwarding of UDP broadcasts for a specific protocol (DHCP uses UDP 67/68), but it does not specify the destination server address; it only permits the forwarding.
- D
ip dhcp-server 172.16.1.100
Why wrong: This is not a valid Cisco IOS command. The correct command to specify a DHCP server is ip helper-address.
Quick Answer
The answer is to configure the `ip helper-address 172.16.1.100` command on R1’s LAN-facing interface, typically GigabitEthernet0/1. This is correct because DHCP relies on broadcast traffic, which routers by default do not forward across subnets; the `ip helper-address` command converts those local broadcasts into unicast packets directed to the specified DHCP server at 172.16.1.100, enabling clients on the 192.168.1.0/24 LAN to obtain IP addresses from a server on a remote subnet reachable via R2. On the CCNA 200-301 v2 exam, this scenario tests your understanding of DHCP relay configuration and the critical distinction between the interface facing the clients (where the helper is applied) versus the interface toward the server. A common trap is applying the command on the wrong interface or forgetting that the helper address must be reachable via a routed path. Remember the memory tip: “Helper on the LAN, server on the other side of the router.”
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.
You are connected to R1 via the console. R1's GigabitEthernet0/0 (10.0.0.1/30) connects to R2 (10.0.0.2/30). Hosts on the LAN (192.168.1.0/24) need DHCP services. The DHCP server is located at 172.16.1.100 on a different subnet reachable via R2. Configure R1 to forward DHCP broadcasts to the DHCP server.
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
ip helper-address 172.16.1.100
The ip helper-address command on the LAN interface forwards DHCP broadcast requests to the DHCP server at 172.16.1.100, allowing clients to obtain IP addresses across subnets.
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.
- ✓
ip helper-address 172.16.1.100
- ✗
ip dhcp relay information option
Why it's wrong here
This command enables the insertion of DHCP relay agent information (Option 82), but does not by itself forward broadcasts to a specific server.
- ✗
ip forward-protocol udp 67
- ✗
ip dhcp-server 172.16.1.100
Why it's wrong here
This is not a valid Cisco IOS command. The correct command to specify a DHCP server is ip helper-address.
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.
✓ip helper-address 172.16.1.100Correct answer▾
Why this is correct
This command, when applied to the LAN-facing interface (GigabitEthernet0/1 or similar), converts the DHCP broadcast into a unicast directed to the DHCP server at 172.16.1.100, enabling cross-subnet DHCP.
✗ip dhcp relay information optionWrong answer — click to see why▾
Why this is wrong here
It is a supporting feature for relay agents, not the primary command to forward DHCP broadcasts.
Why candidates choose this
Candidates may confuse relay agent configuration with the actual forwarding command.
✗ip forward-protocol udp 67Wrong answer — click to see why▾
Why this is wrong here
It is a prerequisite but not sufficient; the ip helper-address is still needed to direct the traffic.
Why candidates choose this
Candidates might think enabling the protocol is enough without specifying the server.
✗ip dhcp-server 172.16.1.100Wrong answer — click to see why▾
Why this is wrong here
The command does not exist; it is a fabrication.
Why candidates choose this
Candidates may guess a command that seems logical but is not real.
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
Command / output trap
This command enables the insertion of DHCP relay agent information (Option 82), but does not by itself forward broadcasts to a specific server.
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 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
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Network Services and Security — study guide chapter
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FAQ
Questions learners often ask
What does this 200-301 question test?
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: ip helper-address 172.16.1.100 — The ip helper-address command on the LAN interface forwards DHCP broadcast requests to the DHCP server at 172.16.1.100, allowing clients to obtain IP addresses across subnets.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on 200-301
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are connected to R1 via the console. R1 is a router that needs to provide DHCP services for hosts on VLAN 10 (192.168.10.0/24) and VLAN 20 (192.168.20.0/24). The DHCP server is located on VLAN 10 at 192.168.10.100, but hosts on VLAN 20 cannot reach it directly. Configure R1 to forward DHCP broadcasts from VLAN 20 to the DHCP server.
medium- ✓ A.interface GigabitEthernet0/0.20 encapsulation dot1Q 20 ip helper-address 192.168.10.100
- B.interface GigabitEthernet0/0.10 encapsulation dot1Q 10 ip helper-address 192.168.10.100
- C.interface GigabitEthernet0/0.20 encapsulation dot1Q 20 ip dhcp relay information option
- D.ip dhcp pool VLAN20 network 192.168.20.0 255.255.255.0 default-router 192.168.20.1
Why A: The ip helper-address command enables the router to forward UDP broadcasts (including DHCP) to a specific server. Placing it on the VLAN 20 subinterface ensures that DHCP requests from VLAN 20 are unicast to the server on VLAN 10.
Last reviewed: Jun 7, 2026
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.
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