Detecting Duplex Mismatch on Ethernet

IEEE 802.3 Ethernet networks, a standard LAN environment, provide a way to auto-negotiate the settings of capacity (10, 100, or 1000Mb/s) and duplex (fullor half-). Under certain conditions described below, the auto-negotiation protocol fails to work properly. The resultant configuration problem, duplex mismatch, appears to be common; when this problem occurs, the connectivity is impaired, but not completely removed. This can result in performance problems that are hard to locate. This paper describes a work in progress aimed at (i) studying the condition of duplex mismatch in IEEE 802.3 Ethernet networks, (ii) producing an analytical model of duplex mismatch, (iii) validating the model, (iv) studying the effects of duplex mismatch on TCP throughput, (v) designing an algorithm for duplex mismatch detection using data from active testing, and (vi) incorporating the detection algorithm into an existing open-source network troubleshooting tool (NDT).