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300-410 Practice Question: Is troubleshooting a DHCPv4 issue where a router…
A network engineer is troubleshooting a DHCPv4 issue where a router configured as a DHCP server is not assigning addresses to clients on a subnet that is reachable via a different router (relay). The relay router (R2) has 'ip helper-address 10.1.1.1' on its client-facing interface, and the DHCP server is at 10.1.1.1 (R1). The engineer sees that R2 is sending DHCP DISCOVER messages with giaddr set to the client-facing interface IP, but R1 is not responding. R1 has a DHCP pool for the client subnet. The engineer pings 10.1.1.1 from R2 successfully. What is the most likely cause?
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 DHCP server does not have a route to the client subnet (the giaddr subnet).
The DHCP server may not have a route back to the client subnet (the giaddr subnet). Even though the server's interface IP is reachable, the server needs to send the OFFER to the giaddr (which is the relay agent's interface IP). If the server does not have a route to that subnet, the OFFER will be dropped. The ping from R2 to R1 succeeds because R1's interface is directly connected, but the return traffic from R1 to the giaddr (which is on a different subnet) may fail if R1 does not have a route.
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 does not have a route to the client subnet (the giaddr subnet).
Why this is correct
Correct because the server sends the OFFER to the giaddr IP, which is on a different subnet; without a route back, the OFFER is lost.
- ✗
The relay agent R2 is missing the 'ip dhcp relay information option' command.
Why it's wrong here
Incorrect because Option 82 is not required for basic relay; its absence does not prevent the server from responding.
- ✗
The DHCP pool on R1 is missing the 'default-router' command.
Why it's wrong here
Incorrect because missing default-router would still allow the server to send an OFFER with an IP address; the client would just not have a gateway.
- ✗
The 'ip helper-address' on R2 should point to the server's loopback address, not the interface IP.
Why it's wrong here
Incorrect because the helper address can be any IP reachable on the server; the interface IP is fine.
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Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
DHCP Relay Configuration
A DHCP relay configuration allows a router to forward DHCP broadcast requests from clients on one subnet to a DHCP server on a different subnet, enabling centralized IP address management across multiple networks.
Key term
DHCP Client and Server
A DHCP client is any device that requests network configuration settings from a DHCP server, which automatically assigns IP addresses and other parameters to devices on a network.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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