Why is the internet not working?

Question

System administration

The situation is this: there is a network in another city (where it is very reluctant to go), there is a server on Windows 2003 with Microsoft Internet Security 2006. It had about six months of uptime, everything worked. Suddenly, on some computers (all computers running Windows XP Professional SP3, by the way) files and mail stopped downloading. Moreover, RDP connects to these computers normally and everything works quickly, but more than 200-300 kilobytes via HTTP, HTTPS, FTP or SMB cannot be downloaded, and even that is wildly slow. I checked one of the computers with the AVZ utility - nothing came up. I tried to disable some ISA rules aimed at protecting the network - I allowed the flood and so on, but it did not work.
Can you suggest which way to dig?

Answer 1

The first thing that comes to mind is the hardware problems of switches / hubs / cards / cables. If no one touched anything in the settings, then it is very likely that you need to start with this.

Answer 2

Sounds like MTU issues + cut ICMP3:4. Small bags are transferred, large ones are not. Maybe the provider “set up” something there?