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. A key principle to apply: a router interface configured as a VLAN default gateway uses the ip helper-address command to forward DHCP broadcasts to a DHCP server on a different subnet.. 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.
Clients: 10.40.40.0/24 in VLAN 40 SVI on distribution switch: 10.40.40.1/24 DHCP server: 172.16.1.10/24 reachable by routing Clients keep sending DHCPDISCOVER and receive no offer.
PCs in VLAN 40 are not receiving addresses from the centralized DHCP server at 172.16.1.10. What should be configured on the VLAN 40 default gateway interface?
Clients: 10.40.40.0/24 in VLAN 40 SVI on distribution switch: 10.40.40.1/24 DHCP server: 172.16.1.10/24 reachable by routing Clients keep sending DHCPDISCOVER and receive no offer.
ip dhcp excluded-address 10.40.40.1 10.40.40.10
Why wrong: Distractor.
ip helper-address 172.16.1.10
Correct choice.
service dhcp
Why wrong: Distractor.
ip default-gateway 172.16.1.10
Why wrong: Distractor.
Answer choices
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 172.16.1.10
When DHCP clients and the DHCP server are on different subnets, the router interface serving the client subnet must relay broadcasts to the server with the ip helper-address command.
Key principle: A router interface configured as a VLAN default gateway uses the ip helper-address command to forward DHCP broadcasts to a DHCP server on a different subnet.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
ip dhcp excluded-address 10.40.40.1 10.40.40.10
Why it's wrong here
Distractor.
When this WOULD be correct
In a different scenario where the question involves configuring DHCP settings for a specific range of IP addresses on a DHCP server, such as preventing certain addresses from being assigned to clients, this option would be correct. For example, if the question asked how to prevent the DHCP server from assigning addresses within a specific range to avoid conflicts, this would apply.
ip helper-address 172.16.1.10
Why this is correct
Correct choice.
Related concept
A router interface configured as a VLAN default gateway uses the ip helper-address command to forward DHCP broadcasts to a DHCP server on a different subnet.
service dhcp
ip default-gateway 172.16.1.10
Why it's wrong here
Distractor.
When this WOULD be correct
In a different scenario where a question asks for the configuration of a standalone device, such as a router or switch that is not acting as a DHCP relay, specifying 'ip default-gateway 172.16.1.10' would be correct to ensure that the device can route packets to the DHCP server for itself.
Option-by-option analysis
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.
Why this is correct
Correct choice.
Why this is wrong here
The 'ip dhcp excluded-address' command is used on a DHCP server to prevent certain addresses from being assigned, not on a router interface to forward DHCP requests. This command would not help clients in VLAN 40 reach the centralized DHCP server.
★ When this WOULD be the correct answer
In a different scenario where the question involves configuring DHCP settings for a specific range of IP addresses on a DHCP server, such as preventing certain addresses from being assigned to clients, this option would be correct. For example, if the question asked how to prevent the DHCP server from assigning addresses within a specific range to avoid conflicts, this would apply.
Why candidates choose this
Students may think that excluding addresses on the default gateway interface would reserve those addresses for the gateway itself, but this command is only valid on a device acting as a DHCP server, not on a router interface.
Why this is wrong here
The 'service dhcp' command globally enables the DHCP server or relay agent on a Cisco device, but it does not specify where to forward requests. Without the 'ip helper-address' command, DHCP broadcasts will not be forwarded to the server.
★ When this WOULD be the correct answer
If the question were about configuring a router to act as a DHCP server for VLAN 40, then 'service dhcp' would be the correct answer. This would imply that the router is intended to provide IP addresses directly to clients in that VLAN.
Why candidates choose this
Students may confuse 'service dhcp' with enabling DHCP relay functionality, but it only enables the DHCP process; the actual forwarding requires the interface-level 'ip helper-address' command.
Why this is wrong here
The 'ip default-gateway' command is used on a switch to set a default gateway for management purposes, not to forward DHCP broadcasts. It does not provide DHCP relay functionality.
★ When this WOULD be the correct answer
In a different scenario where a question asks for the configuration of a standalone device, such as a router or switch that is not acting as a DHCP relay, specifying 'ip default-gateway 172.16.1.10' would be correct to ensure that the device can route packets to the DHCP server for itself.
Why candidates choose this
The term 'default-gateway' may mislead students into thinking it helps clients reach the DHCP server, but it is only for the device's own management traffic, not for relaying DHCP requests.
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
Ensure you understand the difference between DHCP relay and DHCP security features like snooping, as well as local DHCP server configuration.
Detailed technical explanation
DHCP (Dynamic Host Configuration Protocol) is a network management protocol used to dynamically assign IP addresses and other network configuration parameters to devices on a network. DHCP clients initially send broadcast messages to discover DHCP servers. However, broadcasts are limited to the local subnet and do not traverse routers by default. When clients and the DHCP server reside on different subnets, a mechanism is required to forward these broadcasts across subnet boundaries. The ip helper-address command on a router interface configured as a VLAN default gateway enables DHCP relay. This command instructs the router to forward DHCP broadcast packets received on that interface to the specified DHCP server IP address, in this case, 172.16.1.10. The router converts the broadcast into a unicast message directed at the DHCP server, allowing clients in VLAN 40 to obtain IP addresses from the centralized DHCP server despite being on a different subnet. A common exam trap is confusing DHCP relay with DHCP server configuration or IP address exclusion. Commands like ip dhcp excluded-address only reserve IP addresses from the DHCP pool and do not facilitate relay. Similarly, service dhcp enables the router to act as a DHCP server but does not forward requests to another server. The ip default-gateway command sets a device's default route and does not influence DHCP traffic. Understanding the role of ip helper-address in relaying DHCP requests is critical for correctly configuring VLAN interfaces in multi-subnet environments.
Key takeaway
A router interface configured as a VLAN default gateway uses the ip helper-address command to forward DHCP broadcasts to a DHCP server on a different subnet.
Real-world example
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
Review a router interface configured as a VLAN default gateway uses the ip helper-address command to forward DHCP broadcasts to a DHCP server on a different subnet., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
Network Services and Security — This question tests Network Services and Security — A router interface configured as a VLAN default gateway uses the ip helper-address command to forward DHCP broadcasts to a DHCP server on a different subnet..
The correct answer is: ip helper-address 172.16.1.10 — When DHCP clients and the DHCP server are on different subnets, the router interface serving the client subnet must relay broadcasts to the server with the ip helper-address command.
Review a router interface configured as a VLAN default gateway uses the ip helper-address command to forward DHCP broadcasts to a DHCP server on a different subnet., then practise related 200-301 questions on the same topic to reinforce the concept.
A router interface configured as a VLAN default gateway uses the ip helper-address command to forward DHCP broadcasts to a DHCP server on a different subnet.
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Last reviewed: May 17, 2026
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