| When I was a little boy my Dad taught me that if I want something done right then I should do it manually. With this in mind, another thing I have learned about building networks is something so inconspicuous that it is hardly ever thought of, but it has a direct impact on end-user perception in a way bigger than you would ever imagine. In fact, in doing an infrastructure assessment at a major corporation, I noticed this problem, scheduled to have it corrected and after the change, we received email after email wanting to know what we did to speed up the network. It made that big of a difference! What am I talking about? Something we call, Ethernet duplex mismatch. This problem affects all Ethernet based devices and therefore can be very widespread on even the best maintained networks. Duplex mismatch is caused by having different duplex settings on each side of a connection. To sum up the differences in full vs. half duplex; in full duplex both sides of the connection can send data at once whereas in half duplex mode only one end of the connection can send data. If these rules are broken then you experience duplex mismatch. Basically what happens is that a device auto-detects or is hard-coded to connect at one speed (lets say 100Mbps/Full Duplex) and the other end of the connection is connected at a different speed (100Mbps/Half Duplex) then you experience duplex mismatch and a network collision occurs. In the event of a collision, all devices on an Ethernet network pause for a randomly determined period before attempting to send data again. This drastically affects network performance and can make or break your MetaFrame deployment. The solution to duplex mismatching is to always manually configure network devices for full or half duplex, not allowing for any type of auto-negotiation. From my experiences, auto-negotiation is not reliable enough to run in production. I highly recommend going through the entire environment to verify duplex settings and if needed, manually setting the duplex setting on every Ethernet device and switch port. You will even want to verify the Internet Service Providers duplex settings and set your routers appropriately. I cannot stress this point enough, addressing duplex mismatch will cure huge performance problems and spending the time to configure both the connection speeds and duplex settings on both the device and switch will leave you and your end-users with optimum performance.
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