Quiz Entry - updated: 2026.07.14
What are runts, giants, and CRC (Cyclic Redundancy Check) errors on a switch interface?
Runts are frames under 64 bytes, giants exceed 1,518 bytes, and CRC errors are checksum mismatches — all counted by show interfaces and usually pointing at bad NICs, cabling, or interference.
| Error Type | Description | Common Cause |
|---|---|---|
| Runts | Frames smaller than 64 bytes (minimum Ethernet size) | Malfunctioning NIC (Network Interface Card)s, collisions |
| Giants | Frames larger than 1,518 bytes (maximum Ethernet size) | Malfunctioning NICs, driver issues |
| CRC Errors | Calculated checksum doesn't match received checksum | Electrical interference (EMI (Electromagnetic Interference)), loose/damaged cables, incorrect cabling |
| Input Errors | Sum of all input errors (runts + giants + CRC + no buffer + frame + overrun + ignored) | Various physical/data link issues |
| Output Errors | Sum of all errors preventing frame transmission | Interface congestion, hardware failure |
| Collisions | Frames retransmitted due to Ethernet collision | Normal in half-duplex; should never occur in full-duplex |
| Late Collisions | Collision after 512 bits transmitted | Excessive cable length, duplex mismatch |
Tip: If you see many CRC errors, inspect the physical cable and look for electromagnetic interference sources. If you see late collisions, check for duplex mismatch or cables that exceed the maximum length (100m for Cat5e/6).
Go deeper:
Ethernet frame (Wikipedia) — defines the 64-byte minimum (runts) and ~1518-byte maximum (giants) and the FCS field.- Cyclic redundancy check (Wikipedia) — the polynomial checksum whose mismatch produces a CRC error.