300-410 Infrastructure Services Practice Question
A network engineer is configuring a Cisco IOS router to act as a Dynamic Host Configuration Protocol (DHCP) relay agent. The router receives DHCP broadcast requests on interface GigabitEthernet0/1 and must forward them to a DHCP server at 10.1.1.100. Which command is required to enable this functionality?
⚠ Common exam trap
Many exam-takers confuse the DHCP relay command with the DHCP server pool configuration command, or assuming that ip forward-protocol alone can specify a server address.
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 10.1.1.100
To configure a Cisco IOS router as a DHCP relay agent, you must enable the forwarding of DHCP broadcasts to a specific server. The ip helper-address command on the ingress interface accomplishes this by converting broadcast DHCP requests into unicast packets destined for the configured server. Other options either configure local DHCP server functionality or are invalid commands.
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 10.1.1.100
Why this is correct
The ip helper-address command, configured on the interface receiving the DHCP broadcasts, forwards these UDP broadcasts (ports 67 and 68) to the specified server as unicast packets. This allows a single DHCP server to service multiple subnets without being directly attached to each. It is the correct and standard method for DHCP relay on Cisco IOS.
- ✗
ip dhcp pool 10.1.1.100
Why it's wrong here
The ip dhcp pool command creates a DHCP pool for a local DHCP server, not a relay agent. It is used when the router itself assigns IP addresses to clients. This does not forward requests to an external server, so it is incorrect for the relay scenario.
- ✗
ip dhcp relay 10.1.1.100
Why it's wrong here
There is no Cisco IOS command named ip dhcp relay. DHCP relay is configured using ip helper-address. Some platforms may use different syntax, but on standard Cisco IOS routers, this command is invalid. Thus, it cannot be used to forward DHCP requests to a server.
- ✗
ip forward-protocol udp 10.1.1.100
Why it's wrong here
The ip forward-protocol udp command is used to specify which UDP ports are forwarded when ip helper-address is configured; it does not specify a destination server address. Without ip helper-address, broadcasts are not forwarded. Therefore, this command alone does not enable DHCP relay to a specific server.
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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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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
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