220-1201 Networking Practice Question
A company has a network with multiple VLANs. Users on VLAN 10 need to access a server on VLAN 20, but they cannot. The technician verifies that the switch ports are correctly assigned and the server is reachable from other VLANs. Which of the following is the MOST likely cause?
⚠ Common exam trap
The trap here is assuming a DNS or server configuration issue when the problem is isolated to one VLAN's ability to reach another, which points to inter-VLAN routing or ACLs.
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 router or Layer 3 switch is not configured to route between VLAN 10 and VLAN 20.
Inter-VLAN routing requires explicit configuration on a Layer 3 device. If VLAN 10 cannot reach VLAN 20 while other VLANs can, the routing between those specific VLANs is likely missing or misconfigured. This is the most probable cause given the symptoms. Other options would cause broader connectivity issues.
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 router or Layer 3 switch is not configured to route between VLAN 10 and VLAN 20.
Why this is correct
Inter-VLAN routing must be explicitly configured on a router or Layer 3 switch. If routing between VLAN 10 and VLAN 20 is not enabled, traffic cannot pass between them. The fact that other VLANs can reach the server suggests that routing works for those VLANs but not for VLAN 10. This is the most likely cause.
- ✗
The default gateway on VLAN 10 is misconfigured.
Why it's wrong here
If the default gateway were misconfigured, users on VLAN 10 would not be able to reach any remote network, not just VLAN 20. The scenario states that other VLANs can reach the server, so the gateway on those VLANs is correct. The issue is specific to VLAN 10 to VLAN 20 communication, which points to inter-VLAN routing or ACLs.
- ✗
The subnet mask on the server is incorrect.
Why it's wrong here
An incorrect subnet mask on the server would affect communication with multiple subnets, not just VLAN 10. Since other VLANs can reach the server, the server's subnet mask is likely correct. The problem is isolated to VLAN 10, so the server configuration is not the primary suspect. The issue lies in the path between VLAN 10 and VLAN 20.
- ✗
The DNS server is not resolving the server's hostname for VLAN 10 clients.
Why it's wrong here
DNS resolution issues would prevent access by hostname, but users could still reach the server by IP address. The scenario does not specify whether access is by name or IP. Moreover, DNS problems would affect all VLANs equally, not just VLAN 10. The inability to reach the server at all suggests a routing or firewall issue.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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