Cisco Certified Network Associate (CCNA) Practice Exam

What does it indicate if the line status is up and the protocol status is down?

1. Layer 1 issue

2. Layer 2 issue

3. Configuration mismatch

4. No incoming traffic

The correct answer is: Layer 2 issue

When the line status is up but the protocol status is down, it indicates that the physical layer of the connection is functioning correctly, meaning there is a valid physical link between the devices. However, the protocol layer is experiencing a problem, which may point to a Layer 2 issue. This situation often arises due to issues such as mismatched encapsulation types, VLAN mismatches, or problems with spanning tree protocol. Each of these issues affects how data is being processed at the data link layer, which results in the protocol being down despite the physical connection being good. While it might seem like the issue could stem from configuration mismatches in some cases, the specific indication of the protocol being down while the line status is up firmly situates the problem at Layer 2, where the data link layer must manage how data packets are formatted for transmission over the physical medium.