Some Ethernet interfaces can run full- duplex, allowing information to be transmitted in both directions at the same time. Not only are there different speeds available, there are also different duplex modes. These days, twisted pair Ethernet comes in many different flavors. The upshot: Either trust auto-negotiation or manually configure everything.Unexpected consequences (and why there's no better alternative).How it's supposed to work (and why it sometimes doesn't).The options discussed most thoroughly in this document are 10 megabits per second ( Mbps), 100 Mbps, half-duplex, and full-duplex. This document explains the different ways that varying Ethernet standards communicate with each other and select a common speed and method of data exchange. It was originally intended for University of Illinois at Urbana-Champaign system administrators, and is reprinted with permission from the author, Jay Kreibich. The article offers detailed explanation of how auto-negotiation works, as well as potential pitfalls and references for configuring devices under the most popular OSes. Still, many Cable/DSL modems and some residential broadband routers only work at 10Mbps, half- duplex, and it may be necessary to manually configure your LAN clients. This document addresses, in detail, many current and past issues configuring the speed and duplex of ethernet network devices. Note that the need for hand-congiguring switch port speeds and duplex settings has somewhat decreased since the article was initially published.

Mac ethernet adapters duplex issues