Update: I was eventually able to contact someone at my service provider. They suggested trying to access speedtest.net, which was the first http site I was unable to access. Once they hear this, they "changed something on their end" and "ran a bunch of tests". I wasn't able to get a technical description of what they changed- just "something to help you reach sites". If there's anyone out there who might suggest what it is they changed, I hate not knowing. However, I seem to be able to route all traffic at this point.
1 of 1 people found this helpful
My first guess would be an MTU setting. In today's networks, Ethernet frames of 1500 bytes are generally expected to pass end-to-end without fragmentation. If the maximum frame size is smaller, then ICMP messages tell the endpoints that the frame is too big and a smaller size is negotiated. If both a smaller-than normal MTU exists and a firewall filters the ICMP unreachable messages, you have a scenario where small packets such as traditional ping work, but web sites fail to load.
Google the acronym "PMTUD" (Path Maximun Transmission Unit Discovery) for more details.
As I'm not your service provider and I didn't run a test of MTU on your specific network, this is somewhat of a scientific wild-*** guess but it's most often the problem in cases as you described.
If you have a firewall setting that filters ICMP unreachables you're contributing to the problem but not the root cause of it.