Match each Cisco IOS interface status or error symptom on the left to its most probable underlying root cause on the right.
- Interface is down, line protocol is downA physical Layer 1 issue is present, such as an unplugged cable, damaged pinout, or powered-down remote device.
- Interface is up, line protocol is downA Layer 2 framing issue exists, such as an encapsulation mismatch or missing keepalives.
- Interface is administratively down, line protocol is downThe port is manually disabled in configuration mode via the shutdown command.
- Interface is up, line protocol is up (with rapidly incrementing late collisions)A duplex mismatch exists where the local port operates in half-duplex while the remote host operates in full-duplex.
Answer
Interface down/down matches physical Layer 1 failure; Interface up/down matches Layer 2 encapsulation or keepalive failure; Interface administratively down matches manual shutdown command; Interface up/up with late collisions matches duplex mismatch.
Interface diagnostic states directly correlate with specific OSI layers and configurations: physical cable disconnects cause 'down/down'; Layer 2 framing errors cause 'up/down'; the 'shutdown' command displays 'administratively down'; and late collisions on an active link indicate a duplex mismatch.
Step-by-Step Solution
Key Concept
Cisco IOS Interface Status Diagnostics and Troubleshooting