FastEthernet0/13 'show interface' shows high input errors, many CRC and frame counts. What is the root cause?

High input errors, specifically CRC and frame counts, on a FastEthernet interface strongly indicate physical layer issues. CRC (Cyclic Redundancy Check) errors mean the received frame is corrupted, often due to bad cabling, faulty transceivers, or electromagnetic interference. Frame errors (like giant or runt frames) also point to physical medium problems or duplex mismatches. Local buffer overload would manifest as output drops, not input errors. An err-disabled port on the far end would typically show the local port as down/down or administratively down, not accumulating input errors. Duplicate IP addressing causes connectivity issues and ARP problems, but not physical layer input errors like CRC or frame errors.