300-440 Question 277
Single answerA network administrator is troubleshooting an issue where IPv4 hosts in VLAN 10 are unable to obtain an IP address via DHCP. The DHCP server is configured on a different subnet, and the router on the local subnet is configured as the DHCP relay agent. The administrator verifies that the router's interface for VLAN 10 is configured correctly and that the DHCP server is operational. Which of the following could be the root cause of the issue?
- A
The ip helper-address command is missing on the router interface for VLAN 10.
- B
The DHCP server does not support Option 82.
- C
The DHCP relay agent is not configured with the correct default gateway.
- D
The DHCP client devices in VLAN 10 are configured with static IP addresses.
Show answer and explanation
Correct answer: A
Explanation
The ip helper-address command is essential for forwarding DHCP requests from clients in one subnet to a DHCP server in another subnet. Without this configuration, the router will not act as a relay agent, and DHCP packets will not reach the server, causing the issue described in the scenario.
- A. Correct.
The ip helper-address command is required on the router interface to forward DHCP packets to the remote DHCP server. Without it, DHCP Discover messages from clients will not reach the server, causing the issue.
- B. Incorrect.
Although some DHCP servers support Option 82 (DHCP relay agent information), it is not mandatory for basic DHCP functionality. Lack of support for Option 82 would not prevent clients from receiving IP addresses entirely.
- C. Incorrect.
The DHCP relay agent does not require a default gateway configuration to forward packets. It simply forwards DHCP requests using the helper address.
- D. Incorrect.
If the DHCP clients are configured with static IP addresses, they would not send DHCP Discover packets. However, the scenario specifies that the issue is with obtaining IP addresses via DHCP, making this option irrelevant.