Cisco Certified Network Associate (CCNA) Practice Exam

If a ping fails, which command should be used next to check the OSI layers?

1. show interfaces

2. show ip interface brief

3. debug ip packet

4. check routing table

The correct answer is: show ip interface brief

Using the command to display a brief summary of IP interfaces is a strategic step when troubleshooting network connectivity issues such as a failed ping. This command provides a quick overview of the state of interfaces on a router or switch, revealing whether they are up or down. In the context of the OSI model, it primarily relates to the Data Link layer, where the physical status of interfaces is crucial for connectivity. The information displayed by this command helps in identifying if the issue lies with the interface itself, such as being administratively down or not receiving any data link signals. By confirming the operational status of the interfaces, you can ascertain whether the physical and data link layers are functioning correctly, which is fundamental before investigating higher layers of the OSI model. Analyzing the output can also highlight misconfigured IP addresses or subnet masks that might lead to connectivity issues, further affecting the Network layer. Therefore, starting with this command is efficient in narrowing down potential problems related to interface configurations and statuses before diving deeper into other diagnostic commands or layers.