300-410 Question 239
Single answerA network engineer is configuring DHCP services on a Cisco router to assign IP addresses to clients in a branch office. The branch office has multiple VLANs, and the router is configured with subinterfaces for each VLAN. The engineer notices that clients in one of the VLANs are not receiving IP addresses. What is the most likely issue?
- A
The DHCP pool for the affected VLAN is not configured on the router.
- B
The router's subinterface for the affected VLAN is missing the 'ip helper-address' command.
- C
The affected VLAN does not have an SVI (Switched Virtual Interface) configured on the router.
- D
The DHCP server is configured with incorrect lease times for the affected VLAN.
Show answer and explanation
Correct answer: B
Explanation
The issue arises because the router's subinterface for the affected VLAN does not have the 'ip helper-address' command configured. This command is required to relay DHCP requests from clients in that VLAN to the DHCP server. Without it, clients will not receive IP addresses. The other options either do not apply to this scenario or are less likely causes of the problem.
- A. Incorrect.
If the DHCP pool for the affected VLAN is not configured, no IP addresses can be assigned. However, the scenario does not state that the DHCP pool is missing, so this is less likely.
- B. Correct.
The 'ip helper-address' command is required on the router's subinterface for the VLAN to forward DHCP requests to a DHCP server. Without it, clients in that VLAN will not receive IP addresses.
- C. Incorrect.
An SVI is not necessary for DHCP services when subinterfaces are used on the router. Subinterfaces already provide Layer 3 connectivity for VLANs.
- D. Incorrect.
Incorrect lease times would not prevent clients from receiving IP addresses entirely. They might cause other issues, such as IP address exhaustion, but not the described problem.