A network technician observes high counts of late collisions and Frame Check Sequence (FCS) errors on a switch interface connected to a server. A CLI check shows the interface output below:
text
FastEthernet0/1 is up, line protocol is up (connected)
Full-duplex, 100Mb/s, media type is 100BaseTX
542 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
1243 output errors, 891 late collisions
Which physical or data-link issue is the most likely cause of these interface error statistics?
- A duplex mismatch between the switch interface and the connected deviceAnswer
- BSelecting an incorrect Ethernet cable pinout type for the connection
- CA mismatch between the native VLAN IDs configured on the interconnected interfaces
- DMisinterpretation of Layer 2 discovery neighbor information from CDP or LLDP messages
Answer
A duplex mismatch between the switch interface and the connected device is the primary cause of late collisions and FCS errors.
A duplex mismatch occurs when one end of an Ethernet link operates in full-duplex while the opposite end operates in half-duplex. The full-duplex device transmits data whenever ready without checking for carrier activity. When the half-duplex device is transmitting and receives data from the full-duplex device after sending its initial 64 bytes, it records a late collision.
Step-by-Step Solution
Key Concept
Duplex Mismatch Symptoms and Interface Error Counters