CCNA Network Infrastructure and Connectivity Practice Question
A network engineer is configuring a new Cisco switch that will carry traffic for multiple VLANs between two buildings. The link between the two switches must transport frames for VLAN 10, 20, and 30, and both switches must be able to identify which VLAN each frame belongs to. Which configuration should be applied to the inter-switch link on both switches?
⚠ Common exam trap
The trap here is assuming that any trunk encapsulation works, when only the standards-based 802.1Q option is appropriate on modern Cisco switches.
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
✓
Configure the ports as trunk ports using 802.1Q encapsulation.
The inter-switch link must carry frames for multiple VLANs while preserving VLAN identity, which is exactly what an 802.1Q trunk does. Access ports serve only one VLAN, ISL is a legacy nonstandard encapsulation, and routed ports operate at Layer 3 and cannot transport VLAN-tagged frames. Configuring 802.1Q trunking on both ends ensures frames for VLAN 10, 20, and 30 are tagged and correctly identified by the receiving switch.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure the ports as trunk ports using 802.1Q encapsulation.
Why this is correct
A trunk port using 802.1Q encapsulation inserts a VLAN tag into each frame so the receiving switch can identify which VLAN the frame belongs to. This allows a single physical link to carry traffic for VLAN 10, 20, and 30 simultaneously. 802.1Q is the standard trunking encapsulation on Cisco switches and is required for multi-VLAN links between switches.
- ✗
Configure the ports as trunk ports using ISL encapsulation.
Why it's wrong here
ISL is a legacy Cisco-proprietary encapsulation that is not supported on many modern Cisco switch platforms and is not an industry standard. Even where supported, it is not the preferred or default encapsulation for inter-switch links. The scenario calls for a standard, widely supported solution, so ISL is not the best choice here.
- ✗
Configure the ports as routed ports with IP addresses in each VLAN subnet.
Why it's wrong here
Routed ports operate at Layer 3 and cannot carry Layer 2 VLAN-tagged frames between switches. Assigning IP addresses to the inter-switch link would not allow VLAN 10, 20, and 30 frames to traverse the link with their VLAN identity intact. Routed ports are used for point-to-point Layer 3 links, not for extending VLANs between switches.
- ✗
Configure the ports as access ports and assign them to VLAN 10.
Why it's wrong here
Access ports carry traffic for a single VLAN and strip any VLAN tag before forwarding frames. If both inter-switch ports were access ports in VLAN 10, frames from VLAN 20 and VLAN 30 would be dropped or misclassified, breaking connectivity for those VLANs. Access mode is intended for end-device connections, not for a trunk that must carry multiple VLANs.
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Related to this question
Learn chapter
Native VLAN Security
Key term
VLAN
A VLAN (Virtual Local Area Network) is a logical grouping of network devices that behave as if they are on the same physical network segment, regardless of their actual physical location.
Key term
802.1Q
802.1Q is the networking standard that allows multiple virtual LANs (VLANs) to share a single physical network link by tagging Ethernet frames with VLAN identification information.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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