The correct configuration requires changing the helper-address on R1 to 192.168.10.1 and narrowing the excluded-address range to 192.168.10.1 192.168.10.10, while on SW1 enabling DHCP snooping globally and for VLAN 10 with interface G0/1 set as trusted. This works because the helper-address must point to the DHCP server itself—here, R1’s own interface IP—rather than a different address, and the excluded range was too broad, blocking all hosts from receiving an IP. On the CCNA 200-301 v2 exam, this tests your ability to configure a DHCP server and relay agent on Cisco IOS-XE while integrating DHCP snooping to prevent rogue server attacks; a common trap is misplacing the helper-address or forgetting that the relay agent forwards to the server’s IP, not the client’s subnet gateway. Remember the memory tip: “Helper points to the server, not the client; exclude only the gateway and a few static hosts, not the whole pool.”
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.
Network Topology
You are connected to R1. Configure DHCP services so that hosts on VLAN 10 (192.168.10.0/24) can obtain IP addresses from R1. Additionally, configure the switch SW1 to prevent rogue DHCP server attacks on that VLAN. The current configuration has a misconfigured helper-address and an excluded-address range that is too broad.
R1#show running-config | section dhcp
ip dhcp excluded-address 192.168.10.1 192.168.10.254
ip dhcp pool VLAN10_POOL
network 192.168.10.0 255.255.255.0
default-router 192.168.10.1
dns-server 8.8.8.8
!
interface GigabitEthernet0/0.10
encapsulation dot1Q 10
ip address 192.168.10.1 255.255.255.0
ip helper-address 10.0.0.2
!
SW1#show running-config | section dhcp
ip dhcp snooping
ip dhcp snooping vlan 10
no ip dhcp snooping information option
interface GigabitEthernet0/1
ip dhcp snooping trust
!
interface GigabitEthernet0/2
ip dhcp snooping limit rate 10
!
A
On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as trusted.
This option correctly fixes the helper-address to point to R1's own IP (the DHCP server) and narrows the excluded range to only the first 10 addresses, preserving addresses for clients. It also correctly configures DHCP snooping on SW1 with the trusted port facing R1, preventing rogue DHCP servers on other ports.
B
On R1, change the helper-address to 192.168.10.255 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set all ports as trusted.
Why wrong: This is incorrect because the helper-address should be the DHCP server's IP (192.168.10.1), not the broadcast address (192.168.10.255). Also, setting all ports as trusted defeats the purpose of DHCP snooping, as it would allow rogue servers on any port.
C
On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.254. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as untrusted.
Why wrong: This is incorrect because the excluded-address range excludes almost all addresses (192.168.10.1 through 192.168.10.254), leaving only the broadcast address for clients, which is not usable. Also, the port facing the DHCP server (R1) must be trusted, not untrusted.
D
On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as untrusted.
Why wrong: This is incorrect because the port facing the DHCP server (R1) must be trusted. Setting it as untrusted would cause DHCP snooping to drop DHCP server messages (OFFER, ACK) from R1, preventing clients from obtaining IP addresses.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as trusted.
The helper-address on R1's subinterface points to 10.0.0.2 instead of the DHCP server's IP (R1 itself, which is the server). The excluded-address range excludes all addresses in the subnet, preventing any host from getting an IP. The fix: change helper-address to 192.168.10.1 (loopback or interface IP of R1), and narrow the excluded range to the first 10 addresses (or just the gateway). On SW1, enable DHCP snooping globally and for VLAN 10, and mark the port facing R1 (G0/1) as trusted; other ports should be untrusted to block rogue servers.
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.
✓
On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as trusted.
Why this is correct
This option correctly fixes the helper-address to point to R1's own IP (the DHCP server) and narrows the excluded range to only the first 10 addresses, preserving addresses for clients. It also correctly configures DHCP snooping on SW1 with the trusted port facing R1, preventing rogue DHCP servers on other ports.
Related concept
Access ports place end devices into a single VLAN.
✗
On R1, change the helper-address to 192.168.10.255 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set all ports as trusted.
Why it's wrong here
This is incorrect because the helper-address should be the DHCP server's IP (192.168.10.1), not the broadcast address (192.168.10.255). Also, setting all ports as trusted defeats the purpose of DHCP snooping, as it would allow rogue servers on any port.
✗
On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.254. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as untrusted.
Why it's wrong here
This is incorrect because the excluded-address range excludes almost all addresses (192.168.10.1 through 192.168.10.254), leaving only the broadcast address for clients, which is not usable. Also, the port facing the DHCP server (R1) must be trusted, not untrusted.
✗
On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as untrusted.
Why it's wrong here
This is incorrect because the port facing the DHCP server (R1) must be trusted. Setting it as untrusted would cause DHCP snooping to drop DHCP server messages (OFFER, ACK) from R1, preventing clients from obtaining IP addresses.
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.
✓On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as trusted.Correct answer▾
Why this is correct
This option correctly fixes the helper-address to point to R1's own IP (the DHCP server) and narrows the excluded range to only the first 10 addresses, preserving addresses for clients. It also correctly configures DHCP snooping on SW1 with the trusted port facing R1, preventing rogue DHCP servers on other ports.
✗On R1, change the helper-address to 192.168.10.255 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set all ports as trusted.Wrong answer — click to see why▾
Why this is wrong here
The helper-address must be a unicast IP address of the DHCP server, not a broadcast address. Additionally, only ports connected to legitimate DHCP servers should be trusted; all other ports must be untrusted to block rogue servers.
Why candidates choose this
Candidates might think the broadcast address is acceptable because DHCP uses broadcasts, but the helper-address must be a specific server IP. Also, they may mistakenly believe that trusting all ports simplifies configuration without understanding the security risk.
✗On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.254. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as untrusted.Wrong answer — click to see why▾
Why this is wrong here
The excluded-address range should only reserve a few addresses (e.g., for the gateway and static assignments), not the entire subnet. The port connected to the DHCP server must be trusted to allow DHCP server messages; untrusted ports block such messages.
Why candidates choose this
Candidates may think excluding a large range is safe or that the server port should be untrusted to prevent attacks, but this would block legitimate DHCP offers from the server.
✗On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as untrusted.Wrong answer — click to see why▾
Why this is wrong here
DHCP snooping requires that ports connected to legitimate DHCP servers be configured as trusted. Untrusted ports are for client-facing ports where rogue servers might appear; they drop DHCP server messages.
Why candidates choose this
Candidates may confuse the roles of trusted and untrusted ports, thinking that the server port should be untrusted to be more secure, but this breaks DHCP functionality.
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.
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.
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 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.
Network Services and Security — This question tests Network Services and Security — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: On R1, change the helper-address to 192.168.10.1 and the excluded-address range to 192.168.10.1 192.168.10.10. On SW1, enable DHCP snooping globally and for VLAN 10, and set interface G0/1 as trusted. — The helper-address on R1's subinterface points to 10.0.0.2 instead of the DHCP server's IP (R1 itself, which is the server). The excluded-address range excludes all addresses in the subnet, preventing any host from getting an IP. The fix: change helper-address to 192.168.10.1 (loopback or interface IP of R1), and narrow the excluded range to the first 10 addresses (or just the gateway). On SW1, enable DHCP snooping globally and for VLAN 10, and mark the port facing R1 (G0/1) as trusted; other ports should be untrusted to block rogue servers.
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.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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 →
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. Drag and drop the following steps into the correct order to configure a Cisco IOS-XE router as a DHCP server for a client VLAN and then enable a DHCP relay agent on a different interface to forward client requests to a remote server.
hard
A.Enter global configuration mode, create the DHCP pool, configure the network and default gateway, exclude addresses, enable DHCP relay on the required interface, and verify.
✓ B.Enter global configuration mode, enable DHCP relay on the required interface, create the DHCP pool, configure the network and default gateway, exclude addresses, and verify.
✓ C.Enter global configuration mode, create the DHCP pool, enable DHCP relay on the required interface, configure the network and default gateway, exclude addresses, and verify.
✓ D.Enter global configuration mode, exclude addresses, create the DHCP pool, configure the network and default gateway, enable DHCP relay on the required interface, and verify.
Why B: The correct order is to first exclude addresses to prevent the DHCP server from leasing reserved or gateway IPs, then create and configure the DHCP pool (network, default gateway), next enable DHCP relay on the required interface, and finally verify. Option D follows this Cisco best practice. Option A risks assigning excluded addresses because the pool is created before exclusions. Options B and C place relay setup before the pool is fully configured, which is incorrect.
Variation 2. Drag and drop the following steps into the correct order to configure a Cisco IOS-XE router as a DHCP relay agent and verify the DHCP DORA process for a client on a different subnet.
medium
✓ A.Configure the 'ip helper-address' command on the interface facing the client subnet.
✓ B.Verify DHCP relay operation using 'show ip interface' and 'show ip dhcp relay'.
✓ C.Trigger the DORA process on the client by releasing and renewing the IP address.
✓ D.Use 'debug ip dhcp relay' to observe the DORA packets being forwarded.
Why A: First configure the ip helper-address on the client-facing interface (A). Then enable 'debug ip dhcp relay' (D) so forwarded packets are captured. Next trigger the DORA process by releasing/renewing the client IP address (C). Finally verify with passive show commands (B). Debug must be active before the DORA exchange; enabling it afterward misses the output.
Last reviewed: Jun 6, 2026
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