LFCS Networking Practice Question
You manage a Linux server that provides DHCP services to a small office network using the dhcpd daemon. The server has two network interfaces: eth0 (192.168.1.1/24) serving the internal network, and eth1 (192.168.0.1/24) connected to a DMZ. The DHCP server is configured to serve addresses only on eth0. Users on the internal network report that they are not receiving IP addresses. You check the DHCP server and find that the dhcpd service is running and listening on UDP port 67. From a client, you run tcpdump and see DHCPDISCOVER packets being sent, but no DHCPOFFER from the server. You also verify that no firewall rules are blocking DHCP traffic on either side. What is the most likely reason for the failure?
⚠ Common exam trap
Test-takers frequently assume a running service with an open port (UDP 67) is sufficient to serve DHCP, but the dhcpd daemon requires explicit subnet declarations to process requests on each interface.
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 dhcpd configuration file does not have a subnet declaration for the 192.168.1.0/24 network.
The dhcpd daemon will only respond to DHCPDISCOVER packets on interfaces for which it has a matching subnet declaration in its configuration file (typically /etc/dhcp/dhcpd.conf). Without a subnet declaration for 192.168.1.0/24, dhcpd ignores all DHCP traffic on eth0, even though the service is running and listening on UDP port 67. The absence of DHCPOFFER packets despite seeing DHCPDISCOVERs confirms that the server is not processing the requests for that subnet.
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 DHCP server's IP address is not in the same subnet as the clients.
Why it's wrong here
The server's IP is 192.168.1.1, which is in the same subnet, so this is not an issue.
- ✓
The dhcpd configuration file does not have a subnet declaration for the 192.168.1.0/24 network.
Why this is correct
Without a subnet declaration, the DHCP server does not know which pool to offer addresses from and will ignore broadcasts on that subnet.
- ✗
The dhcpd service is not running.
Why it's wrong here
The stem says it is running.
- ✗
The network switch is blocking broadcast packets.
Why it's wrong here
The client can send DHCPDISCOVER, and broadcasts are generally allowed on a switch.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.