Q

Can you please explain the following, common Ethernet errors?

Can you please explain the following, common Ethernet errors?

  • Short/Runt frames
  • Jabbers
  • CRC/FCS errors
  • Late collision
  • Misaligned frames

I'll begin with some basics about how Ethernet networks work before explaining these errors. First, Ethernet networks have both a minimum (64 bytes) and a maximum (1,518 bytes) frame size. The number of bytes in a packet must always be divisible by eight.

Second, Ethernet uses checksums to validate that a packet sent from one host is the same packet received by the recipient host(s). The validation mechanism used by Ethernet is called the Cyclic Redundancy Check (CRC). The checksum is a value stored in the Ethernet frame called the Frame Check Sequence (FCS).

Finally, Ethernet is a shared medium, and only one set of transmissions can be sent across the segment at any given point in time. Therefore, a host must determine if the Ethernet segment is available before actually sending data. The methodology for determining if an Ethernet segment is available for transmission is called the Carrier Sense Multiple Access/Collision Detect (CSMA/CD).

Given the above, let's look at the different error types.

Short/Runt frames
These are frames that do not meet the 64-bytes minimum frame size.

Oversized frames/Jabbers
These are frames that exceed the 1,518-bytes maximum frame size. They also have an invalid checksum (which happens as a result of the frame being oversized). Jabbers occur when these oversized frames are being continuously sent across the Ethernet by a host, thereby causing the segment to be unusable by other hosts.

CRC/FCS errors
These errors occur when the checksum of an Ethernet frame is no longer valid, and therefore, the frame is no longer considered to be valid

Misaligned frames 
Misaligned frames have a frame size that is indivisible by eight.

Late Collision/Collisions
Collisions are the result of multiple hosts trying to use an Ethernet segment at the same time. As these collisions occur, they cause the frames on the network to become invalid. As a result, collisions are typically accompanied by any or all of the previously discussed errors.

To learn more, check out this article on SearchNetworking.com that offers good insight into Ethernet errors and their causes.

This was first published in August 2005

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