300-410 Infrastructure Services Practice Question
A network engineer is troubleshooting a DHCP relay configuration on a Cisco IOS router. The router is configured with the ip helper-address 10.1.1.1 command on interface GigabitEthernet0/0, but clients on the 192.168.1.0/24 subnet are not receiving IP addresses from the DHCP server at 10.1.1.1. The engineer verifies that the DHCP server is operational and has a pool for 192.168.1.0/24. What is the most likely cause?
⚠ Common exam trap
The trap here is assuming that the DHCP relay configuration is at fault when the issue is actually on the DHCP server side, specifically the lack of a return route to the client subnet.
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 DHCP server does not have a route back to the 192.168.1.0/24 subnet.
The most likely cause is that the DHCP server does not have a route back to the 192.168.1.0/24 subnet. Without a return route, the server cannot send DHCPOFFER messages to the relay agent, so clients never receive an address. The other options are either incorrect syntax or not applicable because the relay agent is typically enabled by default and the helper address is on the correct interface.
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 DHCP relay agent is not enabled globally with the service dhcp command.
Why it's wrong here
On Cisco IOS routers, the DHCP relay agent is enabled by default when the ip helper-address command is configured. The service dhcp command enables the DHCP server and relay functionality, but it is typically on by default. If it were disabled, other DHCP functions would also fail, but the scenario does not indicate that. Thus, this is unlikely to be the cause.
- ✓
The DHCP server does not have a route back to the 192.168.1.0/24 subnet.
Why this is correct
For DHCP relay to work, the DHCP server must have a route back to the client subnet to send the DHCPOFFER. If the server lacks a route to 192.168.1.0/24, it cannot deliver the offer, and clients will not receive addresses. This is a common oversight when the server is on a different subnet and no default gateway or static route is configured.
- ✗
The ip helper-address command must be configured with the subnet mask of the DHCP server.
Why it's wrong here
The ip helper-address command takes only the IP address of the DHCP server; no subnet mask is required. Adding a mask would be invalid syntax. The command simply forwards UDP broadcasts to the specified address. Therefore, this is not a valid cause for the failure.
- ✗
The ip helper-address command is configured on the wrong interface.
Why it's wrong here
The ip helper-address command should be configured on the interface closest to the DHCP clients, typically the interface that receives the DHCP broadcast. In this scenario, GigabitEthernet0/0 is likely the client-facing interface, so it is probably correct. If it were on the wrong interface, clients on that subnet would not be able to reach the DHCP server, but the engineer has verified the server and pool, making this less likely.
Visual reference
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Related to this question
Learn chapter
Device Management and Network Monitoring (SNMP, Syslog, NetFlow)
Key term
DHCP Relay Configuration
A DHCP relay configuration allows a router to forward DHCP broadcast requests from clients on one subnet to a DHCP server on a different subnet, enabling centralized IP address management across multiple networks.
Key term
DHCP Client and Server
A DHCP client is any device that requests network configuration settings from a DHCP server, which automatically assigns IP addresses and other parameters to devices on a network.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 300-410 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 300-410 exam.