Question 503 of 1,389
CCNA Network Services and Security Practice Question
Exhibit
R1# show ip dhcp binding
Bindings from all pools not associated with VRF:
IP address Client-ID/ Lease expiration Type
Hardware address
Total number of bindings = 0
Current number of high bindings = 0
Maximum number of high bindings = 256Refer to the exhibit. A network engineer is troubleshooting a DHCP issue where DHCP clients on the LAN subnet are sending DHCPDISCOVER messages but the DHCP server does not receive them. The output of the show ip dhcp binding command on R1 is shown. What is the most likely cause of the problem?
⚠ Common exam trap
Cisco often tests the concept that the ip helper-address command must be configured on the interface that receives the DHCP client broadcasts (the LAN interface), not on the interface facing the DHCP server, leading candidates to overlook the direction of traffic flow.
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 ip helper-address command is configured on the WAN interface instead of the LAN interface facing the DHCP clients.
The DHCP clients on the LAN subnet are sending DHCPDISCOVER messages, but the DHCP server does not receive them because the ip helper-address command is misconfigured on the WAN interface instead of the LAN interface facing the clients. The ip helper-address command must be applied on the ingress interface (the LAN interface) that receives the broadcast DHCPDISCOVER messages, so that the router can convert the broadcast into a unicast directed to the DHCP server. When placed on the WAN interface, it does not intercept the broadcasts from the LAN clients, and the DHCP server never receives the relayed request.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
DHCP service is disabled on R1.
Why it's wrong here
If the DHCP service were disabled, the show ip dhcp binding command would likely return an error message or a status indicating the service is not running. The fact that the command executes and displays a (empty) binding table proves the service is enabled.
- ✓
The ip helper-address command is configured on the WAN interface instead of the LAN interface facing the DHCP clients.
Why this is correct
The show ip dhcp binding output shows zero bindings because the router is not relaying DHCP broadcasts. For a DHCP relay agent to work, the ip helper-address must be placed on the interface that receives client broadcasts (the LAN interface). Configuring it on the WAN interface sends relay messages toward the server in the wrong direction, so client DISCOVERs never reach the DHCP server.
- ✗
The DHCP pool is configured with a network address that does not match the client subnet.
Why it's wrong here
A mismatched network statement in the DHCP pool would still allow the server to receive DISCOVER messages. The server might offer an IP from the pool (even if it is not on the client's subnet) or log an error, leading to some binding creation attempt. Zero bindings indicate the server never receives the requests.
- ✗
The default-router option is missing from the DHCP pool configuration.
Why it's wrong here
Omitting the default-router option affects the default gateway assignment in the DHCP lease, but does not prevent the server from receiving and responding to DISCOVER messages. Bindings would still be created and appear in the output.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓The ip helper-address command is configured on the WAN interface instead of the LAN interface facing the DHCP clients.Correct answer▾
Why this is correct
The show ip dhcp binding output shows zero bindings because the router is not relaying DHCP broadcasts. For a DHCP relay agent to work, the ip helper-address must be placed on the interface that receives client broadcasts (the LAN interface). Configuring it on the WAN interface sends relay messages toward the server in the wrong direction, so client DISCOVERs never reach the DHCP server.
✗DHCP service is disabled on R1.Wrong answer — click to see why▾
Why this is wrong here
Candidates may think that an empty binding table means the service is off, but the command itself would fail or show a service status if DHCP were truly disabled.
✗The DHCP pool is configured with a network address that does not match the client subnet.Wrong answer — click to see why▾
Why this is wrong here
Candidates often associate 'no addresses assigned' with a pool misconfiguration, but a pool mismatch would not prevent the server from seeing DISCOVER messages and possibly creating failed or erroneous bindings.
✗The default-router option is missing from the DHCP pool configuration.Wrong answer — click to see why▾
Why this is wrong here
Candidates may confuse a missing option with a complete failure of DHCP operation, but IP address leasing is independent of options like default-router.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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Last reviewed: Jul 4, 2026
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