CCNP Infrastructure Practice Question

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 'service dhcp' command is disabled globally on the router.

  Why it's wrong here

  The 'service dhcp' command enables the DHCP server and relay agent functionality on the router. By default, it is enabled. If it were disabled, the router would not process DHCP requests at all, but this is less likely than a missing route. The scenario does not indicate that the service was manually disabled.

• ✓

  The DHCP server is not reachable from the router because a route to 172.16.1.100 is missing.

  Why this is correct

  For DHCP relay to work, the router must have a route to the DHCP server's IP address. If no route exists, the router cannot forward the relayed packets, and clients will not receive addresses. This is a common oversight when configuring relay agents in a new environment.

• ✗

  The 'ip helper-address' command must be configured on the interface facing the DHCP server, not the client-facing interface.

  Why it's wrong here

  The 'ip helper-address' command is correctly applied on the interface facing the clients, as it intercepts client broadcasts and forwards them as unicasts to the DHCP server. Configuring it on the server-facing interface would not capture the client broadcasts. Therefore, this is not the cause of the problem.

• ✗

  The DHCP server is configured to use a different subnet mask than the clients require.

  Why it's wrong here

  A mismatch in subnet mask on the DHCP server would affect the addresses assigned, but it would not prevent clients from receiving any address. The clients would still get an IP address, albeit with incorrect mask. The issue here is that clients are not receiving addresses at all, indicating a relay or reachability problem.