Earlier this week our DSL connection speed dropped big time. The curious part was that the Windows machines were running at full speed, but, the Linux boxes were having problems finding web sites. It had the appearance of a DNS problem or someone was trying to DDoS me. I called Sympatico, but, they only support windows (which is only fair to simplify their support). I was going through a number of online sites and found a possible fix. The D-Link box allows you to define the Primary DNS address. I looked at the Status tab and found the DNS IP address and went back to HOME/WAN tab and put in the DNS address and the speed problem on the Linux boxes disappeared.
I dropped a short note to Sympatico describing the fix and they are now looking at putting that information into their knowledge base for others who have the problem (and are not running Windows). If anyone has a technical description of why I will put it up here.