We have a network with a SBS2003 server that connects to an ADSL router and clients connect to the internet via ISA. My PC connects directly to the router (in case of server failure). It has been running this way for 18 months or so just fine but in the last few weeks internet access has been very slow. Any site that requires much bandwidth times out.
A repeatable website indicator is youtube (No significance to youtube except that I can get it to reliably repeat my experiments). With the server connected to the router even my pc (which is not connected through the server) cannot view a youtube video. If I unplug the server my pc gets straight through. This is the same for many other websites.
The server is not using much bandwidth. I have noticed that if I disable the Microsoft firewall service then my pc can get through but I suspect this is just because nothing can get to the router without this running.
I have changed the ADSL router for another unit and there was no change. Our router download speed is around 25 MB/s if the server is not connected.
I have had a suggestion that something in the server may be pinging the router continously which won't show up as bandwidth use but will keep the router busy? If so what would do this? Any other ideas?