A company uses a VLAN-based network with VLAN 10 for sales and VLAN 20 for engineering. Both VLANs are configured on multiple switches. However, hosts in VLAN 10 on Switch1 cannot ping hosts in VLAN 10 on Switch2. Switch1 and Switch2 are connected via a trunk port configured with switchport mode trunk. What is the most likely cause?
Correct Answer: B
Detailed Explanation: In a VLAN environment, simply configuring a trunk port between switches is not enough for hosts in the same VLAN to communicate across switches. The VLAN itself must be created and active on both switches to ensure that VLAN-tagged traffic is recognized and forwarded correctly. If VLAN 10 does not exist on Switch2, the switch will drop incoming frames tagged with VLAN 10 because it doesn’t recognize the VLAN ID. This will prevent devices in VLAN 10 on Switch2 from communicating with devices on VLAN 10 on Switch1, causing failed pings. Option A is plausible if the trunk was limited in allowed VLANs, but the question states the trunk is configured properly. Option C would mean no trunk exists, but the question says the trunk is configured correctly on both sides. Option D is unlikely because Spanning Tree would block a port entirely, causing all traffic to stop; however, hosts in VLAN 10 on the same switch should still ping each other. VLANs must be consistently created and active on all switches that forward traffic for that VLAN. Network administrators typically configure VLAN databases or use dynamic VLAN management protocols like VTP (VLAN Trunking Protocol) to synchronize VLANs across switches. Without the VLAN existing on both switches, frames for that VLAN are dropped.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.