CCNA Interview Questions: MAC and IPv4 Addressing

CCNA IPv4 interview questions often connect Layer 2 MAC addressing with Layer 3 logical addressing. This guide explains the essential facts and corrects several common misconceptions.

Continue with our complete CCNA interview guide and the Cisco 200-301 Premium PDF with the latest available questions and answers.

1. What is a MAC address?

A MAC address identifies a network interface at the data-link layer. Ethernet MAC addresses are normally 48 bits and are written as twelve hexadecimal digits.

2. What does BIA mean?

Burned-In Address refers to the hardware MAC address assigned to an interface by its manufacturer. Some systems can use a locally administered address, so a MAC address should not be described as permanently unchangeable.

3. How is a MAC address organized?

The first portion normally identifies the organization that registered the address block, while the remaining portion identifies an interface within that allocation.

4. How can you view a MAC address?

On Windows, use ipconfig /all or getmac. On Cisco devices, show interfaces displays interface hardware addresses and show mac address-table displays learned mappings.

5. Why is an IP address called logical?

An IP address represents a device’s location within a logical network. It can be assigned manually or dynamically and may change when the device moves to another network.

6. What is the size of an IPv4 address?

IPv4 addresses contain 32 bits and are commonly written as four decimal octets separated by dots.

7. What are the private IPv4 ranges?

• 10.0.0.0/8
• 172.16.0.0/12
• 192.168.0.0/16

These ranges are not routed on the public internet and are commonly translated through NAT.

8. What is APIPA?

Automatic Private IP Addressing uses the link-local range 169.254.0.0/16. A host may select an address from this range when it cannot obtain an IPv4 address from DHCP.

9. What is a default gateway?

The default gateway is the router address a host uses to reach remote networks. The gateway must be reachable on the host’s local subnet.

10. How do MAC and IP addresses work together?

The IP packet keeps its source and destination IP addresses across routed hops. Ethernet headers are rebuilt on each local segment using the MAC addresses for the next-hop delivery.

Interview Preparation

Practice converting prefix lengths to subnet masks and explaining how a host determines whether a destination is local. Use ipconfig, arp -a, ping, and Cisco show commands to verify each answer in a lab.

IPv4 Troubleshooting Example

If two hosts cannot communicate, compare their IPv4 addresses and subnet masks first. Determine whether each host considers the other local or remote. For local communication, verify ARP and switch MAC learning. For remote communication, confirm the default gateway and routing table. Duplicate addresses, incorrect masks, and missing gateways are common interview scenarios.

Verification Checklist

Use ipconfig /all, arp -a, ping, tracert, show ip interface brief, and show arp. Explain what each command proves instead of simply listing commands.