I don't know of any evidence that the Internet as a whole suffered outages due to 9/11, but I can certainly believe that individual web sites and/or ISPs would

I don't know of any evidence that the Internet as a whole suffered outages due to 9/11, but I can certainly believe that individual web sites and/or ISPs would have struggled. Maybe your ISP didn't have a fast enough backbone connection to support all of its customers, or maybe one of its internal routers became overloaded. Or maybe it literally didn't have enough phone lines to support all of the customers simultaneously dialing in.