CCNA Network Infrastructure and Connectivity Practice Question
Which three of the following are characteristics of Layer 2 Ethernet switches that support VLANs? (Choose three.)
⚠ Common exam trap
Cisco often tests the misconception that switches use ARP or that VLANs segment collision domains, when in fact VLANs segment broadcast domains and switches forward based on MAC addresses, not IP addresses.
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
✓
They forward frames based on the destination MAC address.
Layer 2 Ethernet switches that support VLANs forward frames based on the destination MAC address, which is the fundamental switching decision. They can segment a LAN into multiple broadcast domains because each VLAN creates its own isolated broadcast domain, preventing unnecessary traffic propagation. They use the Spanning Tree Protocol (STP) to prevent Layer 2 loops by dynamically blocking redundant paths, ensuring a loop-free topology.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
They forward frames based on the destination MAC address.
Why this is correct
Layer 2 switches operate at the data link layer and make forwarding decisions by inspecting the destination MAC address in the Ethernet frame header. They maintain a MAC address table (CAM table) that maps source MAC addresses to switch ports, allowing them to intelligently forward frames only out the appropriate port rather than flooding to all ports, except for unknown unicast and broadcast frames.
- ✓
They can segment a LAN into multiple broadcast domains.
Why this is correct
By implementing virtual LANs (VLANs), a Layer 2 switch can partition its physical ports into multiple broadcast domains, confining broadcast, multicast, and unknown-unicast traffic to only those ports assigned to the same VLAN. Without VLAN configuration, the entire switch functions as a single broadcast domain, but this VLAN capability is a fundamental Layer 2 feature that lets an administrator logically segment a LAN within one device.
- ✗
They use ARP to resolve IP addresses to MAC addresses.
Why it's wrong here
ARP is a protocol that operates between the network layer and the data link layer, and its role is to resolve a known IP address to a MAC address. However, ARP is not a characteristic of a Layer 2 switch's forwarding process; it is performed by end hosts or by the switch itself only when it needs to communicate as an IP host, such as for management purposes. A pure Layer 2 switch does not use ARP when forwarding frames, because forwarding decisions rely solely on the MAC addresses already contained in the Ethernet frame.
- ✓
They use the Spanning Tree Protocol to prevent Layer 2 loops.
Why this is correct
Spanning Tree Protocol (STP) is a Layer 2 protocol that runs on switches to create a loop-free logical topology from a physically redundant network. It elects a root bridge and places redundant ports into a blocking state, thereby preventing broadcast storms and MAC address table instability caused by Layer 2 forwarding loops. This protocol is essential for the correct operation of enterprise switches that have multiple interconnecting links.
- ✗
They perform routing between VLANs without a router.
Why it's wrong here
Routing between VLANs requires inter-VLAN routing, which is a Layer 3 function. A pure Layer 2 switch lacks the routing table and routed interfaces necessary to forward packets between different subnets; it only forwards Ethernet frames within the same broadcast domain. To route between VLANs, you would need a router on a stick with 802.1Q trunking, or a multilayer switch with switched virtual interfaces (SVIs), not a basic Layer 2 switch.
- ✗
They forward frames based on the destination IP address.
Why it's wrong here
A switch that forwards frames based on the destination IP address is performing Layer 3 routing, a task beyond the capability of a Layer 2 switch. Layer 2 switches examine only the Ethernet destination MAC address and use the CAM table to determine the egress port; they never rewrite or inspect IP headers. When an unknown destination MAC is received, the switch floods the frame, but it still never looks at the IP layer, which further demonstrates that IP address forwarding is not a Layer 2 characteristic.
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
Go deeper
Related to this question
Learn chapter
IPv4 Addressing and Address Classes
Key term
CAN
A CAN (Controller Area Network) is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other without a host computer.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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