These CCNA switching interview questions focus on Ethernet switching, MAC address learning, VLANs, trunking, and basic troubleshooting. Strong candidates explain both the definition and what they would verify on a Cisco device.
For additional practice, see the 200-301 CCNA Premium PDF with the latest available questions and answers.
1. How does a switch learn MAC addresses?
A switch reads the source MAC address of each incoming Ethernet frame and associates it with the ingress port and VLAN in its MAC address table. Dynamic entries age out when they are not refreshed.
2. What is a CAM table?
CAM stands for Content Addressable Memory. On an Ethernet switch, the term commonly refers to the hardware table used to store MAC-address-to-port mappings for fast Layer 2 forwarding.
3. What happens when the destination MAC address is unknown?
The switch floods an unknown unicast frame through all eligible ports in the same VLAN except the incoming port. When the destination responds, the switch learns its source MAC address.
4. How many collision domains does a switch create?
Each switch port is a separate collision domain. A 24-port switch can therefore provide up to 24 collision domains. With full-duplex switched Ethernet, collisions do not normally occur.
5. How many broadcast domains are on a switch?
By default, all ports in the same VLAN belong to one broadcast domain. Each additional VLAN creates another broadcast domain. Communication between VLANs requires Layer 3 routing.
6. What is a VLAN?
A VLAN is a logical Layer 2 network that groups switch ports into a separate broadcast domain. VLANs improve segmentation, security, and network organization without requiring separate physical switches.
7. What is an access port versus a trunk port?
An access port normally carries traffic for one VLAN and sends untagged Ethernet frames to the endpoint. A trunk carries multiple VLANs between network devices, usually using IEEE 802.1Q tags.
8. What is the native VLAN?
On an 802.1Q trunk, native-VLAN frames are transmitted untagged by default. The native VLAN must match on both ends of the trunk to avoid connectivity and security problems.
9. What does line protocol down indicate?
If an interface is administratively up but its line protocol is down, investigate Layer 2 conditions such as encapsulation, keepalives, VLAN state, or the remote side. If both interface and line protocol are down, begin with Layer 1 issues such as cabling, power, transceivers, and port state.
10. Which commands help troubleshoot switching?
show interfaces status
show interfaces switchport
show mac address-table
show vlan brief
show interfaces trunk
show spanning-treeUse command output to form a hypothesis, change one item at a time, and verify the result.
Interview Preparation Tips
- Explain why a switch floods, filters, or forwards a frame.
- Relate every MAC-table entry to a port and VLAN.
- Be ready to calculate broadcast domains from a diagram.
- Know how access and trunk ports handle VLAN traffic.
- Support answers with relevant show commands.
Continue with our Cisco CCNA notes, hands-on labs, and the Cisco 200-301 Premium PDF for structured revision.
Quick Switching Troubleshooting Checklist
When a switching question describes a fault, begin with the physical link and interface status. Confirm speed and duplex, check the VLAN assignment, and verify that trunk links allow the required VLAN. Review the MAC address table to see whether the switch is learning addresses on the expected ports. For inter-VLAN connectivity, also verify the default gateway and Layer 3 routing. Useful commands include show interfaces status, show interfaces trunk, show vlan brief, show mac address-table, and show spanning-tree. A structured sequence helps you explain both the likely cause and the next verification step.