300-410 Infrastructure Services Practice Question
A network engineer is configuring a Cisco IOS XE router to act as a DHCP relay agent. The router receives DHCP discover messages on interface GigabitEthernet0/1 and must forward them to a DHCP server at 10.1.1.100. The engineer configures the command 'ip helper-address 10.1.1.100' on GigabitEthernet0/1. However, the DHCP server is not receiving the requests. Which additional configuration is required to ensure that DHCP relay works correctly?
⚠ Common exam trap
The trap here is focusing on DHCP-specific commands like 'service dhcp' or relay information options, while overlooking the fundamental requirement of IP reachability 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
✓
Ensure that the interface facing the DHCP server has an IP address and that routing is configured to reach 10.1.1.100.
The DHCP relay agent uses the 'ip helper-address' command to forward broadcast DHCP requests to a unicast address. However, the router must have a valid route to that unicast address. If the interface toward the DHCP server is not configured with an IP address or is down, or if there is no route to the server, the relayed packets cannot be sent. Therefore, ensuring IP connectivity to the DHCP server is essential. The other options are either default behaviors or optional features not required for basic relay operation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure 'ip forward-protocol udp 67' globally.
Why it's wrong here
The 'ip forward-protocol udp 67' command is used to specify which UDP ports are forwarded by the helper address. By default, the helper address forwards UDP ports 67 (DHCP server) and 68 (DHCP client), as well as TFTP, DNS, and others. Explicitly configuring port 67 is usually unnecessary because it is already included in the default forwarding list. If the default forwarding were altered, this might be needed, but the scenario does not indicate that. Therefore, this is not the typical additional configuration required.
- ✗
Configure 'ip dhcp relay information option' globally.
Why it's wrong here
The 'ip dhcp relay information option' command enables the DHCP relay agent to insert the client's interface information into the DHCP request. This is used for security and address assignment based on port, but it is not required for basic DHCP relay functionality. The DHCP server can respond without this option. While it can be useful in some scenarios, it is not the missing piece that would prevent the server from receiving requests altogether.
- ✗
Enable 'service dhcp' globally on the router.
Why it's wrong here
The 'service dhcp' command enables the DHCP server and relay agent functionality on the router. In most Cisco IOS XE versions, this service is enabled by default. If it were disabled, the relay agent would not function. However, the scenario states that the engineer configured the helper address, implying that basic IP routing is working. The missing piece is likely related to the DHCP broadcast handling. While 'service dhcp' is important, it is not the additional configuration typically required when the relay agent is not forwarding requests, as it is on by default.
- ✓
Ensure that the interface facing the DHCP server has an IP address and that routing is configured to reach 10.1.1.100.
Why this is correct
This is correct. For the DHCP relay agent to forward requests to the server, the router must have a route to the DHCP server's IP address. The helper address itself only specifies the destination; the router must be able to reach that destination via its routing table. If the interface facing the server is down or lacks an IP address, or if there is no route to 10.1.1.100, the relayed packets will be dropped. This is a common oversight when configuring DHCP relay.
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Related to this question
Learn chapter
BGP Route Selection and Policy
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.
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.
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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.