LPIC-2 Advanced Networking Configuration Practice Question
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?
⚠ Common exam trap
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.
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
✓
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.
Answer analysis
Option-by-option breakdown
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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