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200-901 Practice Question: A company has two Cisco Catalyst switches, SW1…
A company has two Cisco Catalyst switches, SW1 and SW2, connected via a trunk link using port GigabitEthernet0/1 on both switches. SW1 is the root bridge for all VLANs spanning tree. VLAN 10 users on SW1 report they can access the internet and resources in VLAN 10 on SW2, but cannot reach a critical server in VLAN 20 connected to SW2. The server in VLAN 20 has a static IP address and can communicate with other VLAN 20 devices on SW2. SW2's configuration for the trunk port includes 'switchport trunk allowed vlan 10,20'. SW1's trunk port configuration is 'switchport trunk allowed vlan 10'. The network administrator has verified that both switches have VLANs 10 and 20 created and that the default gateways are correct. What is the most likely cause of the issue?
⚠ Common exam trap
Cisco often tests the distinction between VLAN existence on a switch and VLAN permission on a trunk port—candidates assume that if a VLAN is created on both switches, traffic will flow, but the trunk allowed list is the gatekeeper.
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
✓
SW1's trunk port is not configured to allow VLAN 20.
SW1's trunk port is configured with 'switchport trunk allowed vlan 10', which explicitly permits only VLAN 10 traffic. Since VLAN 20 is not in the allowed list, frames from VLAN 20 (including traffic to the server) are dropped at the trunk egress on SW1. This prevents SW1 hosts in VLAN 10 from reaching the VLAN 20 server on SW2, even though the trunk is up and both VLANs exist on both switches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
SW1's trunk port is not configured to allow VLAN 20.
Why this is correct
The trunk allowed VLAN list on SW1 only includes VLAN 10, so VLAN 20 traffic is blocked.
- ✗
SW1 is the root bridge for VLAN 20, causing traffic to be blocked.
Why it's wrong here
Being root bridge does not block traffic; STP only prevents loops.
- ✗
The trunk link between SW1 and SW2 is down.
Why it's wrong here
The trunk is up as VLAN 10 traffic works.
- ✗
The server in VLAN 20 has an incorrect IP address configuration.
Why it's wrong here
The server can communicate with other devices in VLAN 20, so IP configuration is correct.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-901 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-901 exam.