mediumMultiple Choice
CCNP Practice Question: Is troubleshooting a DHCP issue where a client is…
A network engineer is troubleshooting a DHCP issue where a client is not receiving an IP address from a Cisco router configured as a DHCP server. The engineer checks the DHCP pool configuration and sees that the network command is configured with the correct subnet. The engineer also verifies that the ip dhcp excluded-address command is not blocking any addresses. However, the client's DHCP discover message is not reaching the router. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the distinction between a router acting as a DHCP server versus a DHCP relay agent, and the trap here is that candidates assume a correctly configured DHCP pool is sufficient, overlooking the requirement for ip helper-address when the client and server are on different subnets.
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 router's interface is not in the same VLAN as the client, and no ip helper-address is configured.
If the client and the router's DHCP server interface are on different VLANs (i.e., different subnets), the DHCP discover broadcast will not cross the Layer 3 boundary unless the router interface has an ip helper-address configured. The ip helper-address command enables the router to convert the broadcast DHCP discover into a unicast and forward it to the DHCP server. Without it, the client's broadcast never reaches the server, even if the DHCP pool is correctly defined.
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 router's interface is configured with the no ip forward-protocol udp bootps command.
Why it's wrong here
The `no ip forward-protocol udp bootps` command disables the forwarding of UDP broadcasts destined for BOOTPS/DHCP port 67 by the relay agent. However, the router here is acting as the DHCP server itself, not as a relay. A local DHCP server receives DHCPDISCOVER broadcasts natively on its directly connected interface, so this command has no effect on the server's ability to see those broadcasts. This option is incorrect because it targets the relay function rather than the local server reception.
- ✓
The router's interface is not in the same VLAN as the client, and no ip helper-address is configured.
Why this is correct
This is correct because DHCP clients use Layer 2 broadcast (destination FF:FF:FF:FF:FF:FF) to send DHCPDISCOVER messages, and broadcasts never cross a Layer 3 boundary by default. If the router's interface is in a different VLAN from the client, the broadcast stays confined to the client's broadcast domain. To reach a DHCP server in another subnet, you must configure an `ip helper-address` on the client's VLAN interface, which converts the broadcast into a unicast (or directed broadcast) to the DHCP server. Without that relay, the router will never receive the DISCOVER because it is not on the same VLAN.
- ✗
The DHCP pool is configured with the wrong default-router option.
Why it's wrong here
The `default-router` option in a DHCP pool sets the gateway address that the client will configure via the DHCPOFFER message. This option does not influence whether the router receives the DHCPDISCOVER or whether the server responds to it. A wrong default-router address would cause the client to have an incorrect gateway after obtaining an address, but it would not prevent the client from being assigned an IP. Therefore, this cannot explain a complete failure to receive broadcast messages.
- ✗
The router's DHCP server is disabled globally with the no service dhcp command.
Why it's wrong here
The global `no service dhcp` command disables both the DHCP server and relay functionality on the router. If this were the cause, the router would not respond to any DHCP requests, but when an engineer attempts to configure a DHCP pool, Cisco IOS displays an error like 'DHCP is disabled on this router' or requires the `service dhcp` command to be enabled. Since the pool is presumably configured and active, the service must be running, making this option unlikely. This option is incorrect because the failure mode would be immediately apparent during configuration, not a silent absence of DHCPDISCOVER reception.
Visual reference
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 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 350-401 exam.