Half-duplex collision domain violation detected

The network is exhibiting behavior, including packet loss, that corresponds to a failure when two devices attempt to use a half-duplex data channel simultaneously.

Recommended action

This message is generated due to an error within a given collision domain. Generally these Ethernet errors occur if the collision domain is overextended, or a device is ignoring collision detection standards:

  • If running 10Mbps half duplex, ensure that no collision domains exceed 2000 meters.
  • If running 100Mbps half duplex, ensure that no cables exceed 100 meters, which will ensure that no collision domains will exceed the 200 meter limit.
  • If hubs are deployed, you will need to reduce link sizes to standard lengths.
  • If switches are deployed, consider disabling collision-detection by switching to full duplex. Remember to test for duplex conflicts after changing configurations.
  • If it is determined that overlong half-duplex links are not in the test path, download and install the latest NIC drivers on any host machines in the test path. Also, set configuration switches on NICs/transceivers from "SQE" to "Normal" mode.

Detailed explanation

Most often, this condition is due to an over-extended collision domain within an Ethernet environment. For example, some ISPs deploy 10Mbp WANs employing 10Mbps Ethernet over fiber. If they set the switch ports to 10Mbps half duplex, and the WAN link exceeds 2000 meters, this condition exists. Since this condition only drops packets for a select few applications, this problem can become very illusive and difficult to diagnose.

Other causes of this condition are: down-level packet drivers on certain NIC cards; use of SQE on Ethernet segments that do not support SQE tests. Generally failures occur on repeaters, hubs and older Ethernet interfaces that fail to properly receive SQE. This results in packet loss, which in turn affects application performance.

Possible secondary messages

  • "May be due to overlong media - 2000m is maximum for 10Mbps Ethernet"
  • "May be due to overlong media - 200m is maximum for 100Mbps Fast Ethernet"
  • "May be due to the use of SQE signal (heartbeat on a MAU/transceiver) with an incompatible device"

Other resources