Ethernet errors

Ethernet errors
6.2.7 This page will define common Ethernet errors.


Knowledge of typical errors is invaluable for understanding both the operation and troubleshooting of Ethernet networks.

The following are the sources of Ethernet error:

• Collision or runt – Simultaneous transmission occurring before slot time has elapsed
• Late collision – Simultaneous transmission occurring after slot time has elapsed
• Jabber, long frame and range errors – Excessively or illegally long transmission
• Short frame, collision fragment or runt – Illegally short transmission
• FCS error – Corrupted transmission
• Alignment error – Insufficient or excessive number of bits transmitted
• Range error – Actual and reported number of octets in frame do not match
• Ghost or jabber – Unusually long Preamble or Jam event

While local and remote collisions are considered to be a normal part of Ethernet operation, late collisions are considered to be an error. The presence of errors on a network always suggests that further investigation is warranted. The severity of the problem indicates the troubleshooting urgency related to the detected errors. A handful of errors detected over many minutes or over hours would be a low priority. Thousands detected over a few minutes suggest that urgent attention is warranted.

Jabber is defined in several places in the 802.3 standard as being a transmission of at least 20,000 to 50,000 bit times in duration. However, most diagnostic tools report jabber whenever a detected transmission exceeds the maximum legal frame size, which is considerably smaller than 20,000 to 50,000 bit times. Most references to jabber are more properly called long frames.

A long frame is one that is longer than the maximum legal size, and takes into consideration whether or not the frame was tagged. It does not consider whether or not the frame had a valid FCS checksum. This error usually means that jabber was detected on the network.

A short frame is a frame smaller than the minimum legal size of 64 octets, with a good frame check sequence. Some protocol analyzers and network monitors call these frames “runts". In general the presence of short frames is not a guarantee that the network is failing.

The term runt is generally an imprecise slang term that means something less than a legal frame size. It may refer to short frames with a valid FCS checksum although it usually refers to collision fragments.

The next page will continue the discussion of Ethernet frame errors.