This LPIC-2 practice question tests your understanding of advanced networking configuration. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A Linux router needs to forward DHCP broadcasts from clients on subnet 192.168.1.0/24 (eth0) to a DHCP server at 10.0.0.5. Which command starts a DHCP relay agent?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
dhcrelay -i eth0 10.0.0.5
Standard DHCP relay agent command.
dhcpd -cf /etc/dhcp/dhcpd.conf
Why wrong: Starts a DHCP server, not relay.
iptables -A INPUT -i eth0 -p udp --dport 67 -j REDIRECT
Why wrong: iptables cannot perform DHCP relay; it redirects to local process.
dnsmasq -i eth0
Why wrong: dnsmasq can provide DHCP server functions, not relay.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
dhcrelay -i eth0 10.0.0.5
The correct command is `dhcrelay -i eth0 10.0.0.5`. This starts the DHCP relay agent (ISC DHCP relay) on interface eth0, listening for DHCP broadcast packets (UDP port 67) from clients on subnet 192.168.1.0/24 and forwarding them as unicast to the DHCP server at 10.0.0.5. The relay agent also relays the server's unicast replies back to the client, enabling DHCP service across subnets without a local DHCP server.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
dhcrelay -i eth0 10.0.0.5
Why this is correct
Standard DHCP relay agent command.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
dhcpd -cf /etc/dhcp/dhcpd.conf
Why it's wrong here
Starts a DHCP server, not relay.
iptables -A INPUT -i eth0 -p udp --dport 67 -j REDIRECT
Why it's wrong here
iptables cannot perform DHCP relay; it redirects to local process.
dnsmasq -i eth0
Why it's wrong here
dnsmasq can provide DHCP server functions, not relay.
Common exam traps
The trap here is that candidates often confuse the DHCP relay agent command with the DHCP server command (`dhcpd`) or assume a firewall rule (`iptables`) can perform relaying, but only `dhcrelay` correctly implements the RFC 1542 relay function by forwarding broadcasts to a specified remote server.
Detailed technical explanation
The DHCP relay agent, defined in RFC 1542, listens for BOOTP/DHCP broadcasts on UDP port 67, inserts the gateway IP address (giaddr) into the packet, and forwards it as a unicast to the configured server. The server uses the giaddr to determine which subnet the client is on and sends a unicast reply back to the relay, which then broadcasts it on the local subnet. In real-world deployments, multiple relay agents can be chained, and the `-a` option in dhcrelay enables agent-circuit-id suboptions for DHCP option 82, which is critical for security and IP assignment in large ISP networks.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
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FAQ
Advanced Networking Configuration — This question tests Advanced Networking Configuration — Read the scenario before looking for a memorised answer..
The correct answer is: dhcrelay -i eth0 10.0.0.5 — The correct command is `dhcrelay -i eth0 10.0.0.5`. This starts the DHCP relay agent (ISC DHCP relay) on interface eth0, listening for DHCP broadcast packets (UDP port 67) from clients on subnet 192.168.1.0/24 and forwarding them as unicast to the DHCP server at 10.0.0.5. The relay agent also relays the server's unicast replies back to the client, enabling DHCP service across subnets without a local DHCP server.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This LPIC-2 practice question is part of Courseiva's free LPI 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 LPIC-2 exam.
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