What is an MTU and why does it matter?
Your MTU, or Maximum Transmission Unit, is a measure of the configured packet size that your computer uses when sending packets of data to other computers. In the context of ADSL, an MTU is commonly set somewhere between 1400 and 1500 bytes. There turn out to be some critical sizes for the MTU, and a variety of performance problems can be caused (for different, but inter-related, reasons) if your MTU is set too high. Contrary to what might seem sensible, lowering your MTU can actually raise your data transfers speeds (up to a point) as a result. The various adverse issues possible when your MTU is too large can include: • Very low download speeds on an otherwise ‘clean’ data path (no packet loss, low latency). • FTP or other file downloads which stall (stop working) after just the first 1-2 kilobytes downloaded (including the downloading of a server file listing in an FTP client, which is actually just another file download and is subject to the same issues) • Situations where some web
