Some of our users are unable to connect to one particular web server (our library catalogue), getting an "Oops! Google Chrome could not connect to..." type message across all browsers. The only thing they seem to have in common is that their IP addresses are all in the range 2.x.x.x or 90.x.x.x from the same ISP.
I vaguely recall the 2.x range having some historical significance but can't find any reference to it.