Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Users in VLAN 10 cannot obtain IP addresses from the DHCP server located in VLAN 20. The router interface for VLAN 10 has an ip helper-address 192.168.20.5 command configured, and users can ping the DHCP server IP (192.168.20.5) from the router. However, users receive APIPA addresses. What is the most likely cause?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
The DHCP server does not have a scope configured for the 192.168.1.0/24 subnet (VLAN 10)
The DHCP server uses the gateway IP (giaddr) in the relayed packet to determine which scope to use. Without a matching scope, the server does not respond.
B
Distractor review
The router's ip helper-address is configured on the wrong interface
The scenario states the helper address is on the VLAN 10 interface; if it were on the wrong interface, users would not reach the DHCP server at all, but they can ping the server from the router.
C
Distractor review
The switch port connecting users is configured as a trunk instead of an access port
A trunk port would still allow traffic in VLAN 10, but if misconfiguration caused the user to be in the wrong VLAN, they might not be in VLAN 10. However, they could still likely reach the DHCP relay if routing works. A trunk misconfiguration is less likely to cause APIPA when the relay is working.
D
Distractor review
The router's ACL is blocking DHCP offers from the server
If an ACL were blocking DHCP replies, the router would still receive them but drop them; however, the users would not get replies, leading to APIPA. But since the helper address is configured, the ACL would need to explicitly block UDP ports 67/68, which is less common than a missing scope.
Common exam trap
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Technical deep dive
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
- Access ports place end devices into a single VLAN.
- Trunk ports carry multiple VLANs between switches.
- Allowed VLAN lists decide which VLANs can cross a trunk.
- Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
- Use show vlan brief to verify access VLANs.
- Use show interfaces trunk to verify trunk state and allowed VLANs.
- Do not treat every same-VLAN issue as a routing problem.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A network engineer needs to connect two switches located 400 meters apart. The cable run includes high electromagnetic interference from nearby machinery. The engineer decides to use fiber optic cabling. Which transceiver type and fiber combination should be used to ensure the link reaches 400 meters while remaining cost-effective?
Question 2
A network engineer is designing a new switched network and needs to ensure that broadcast traffic from one department does not reach another department's workstations. The engineer plans to use VLANs. Which of the following must be configured on the switches to isolate broadcast domains as intended?
Question 3
A security engineer is configuring a site-to-site VPN between two branch offices. The requirement is to encrypt all traffic between the two networks using IPsec. Which IPsec mode should be used to encrypt the entire IP packet including the original header?
Question 4
A network administrator is connecting two switches to increase bandwidth and provide redundancy. Which technology should be used to combine multiple physical links into a single logical link?
Question 5
A network administrator is experiencing issues where unauthorized devices are offering IP addresses to clients, causing connectivity problems. Which security feature should be enabled on switches to prevent this?
Question 6
A network administrator is troubleshooting a connectivity issue and suspects the problem is related to the physical cabling. At which layer of the OSI model should the administrator begin their investigation?
FAQ
Questions learners often ask
What does this N10-009 question test?
Access ports place end devices into a single VLAN.
What is the correct answer to this question?
The correct answer is: The DHCP server does not have a scope configured for the 192.168.1.0/24 subnet (VLAN 10) — Even when the DHCP relay agent (ip helper-address) is correctly configured, the DHCP server must have a scope (range of IP addresses) defined for the subnet from which the request originates. If no scope exists for VLAN 10, the server will not offer an IP address, causing the client to fall back to APIPA.
What should I do if I get this N10-009 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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