A couple of weeks ago, I posted a note speculating that the outage I experienced was due to a problem in the gear Comcast was using to manage peer-to-peer traffic. After correspondence with some of their network engineers, I’m happy to say that I was wrong. Here’s the short form of the explanation:
We encountered a memory limitation on a handful of our core routers in the PA-NJ area triggered by an external routing event. The switching mode of the routers changed in that situation. In this new mode, subscriber traffic was subjected to an internal infrastructure security policy that permitted ping and traceroute but denied TCP traffic. This caused the discrepancy of website reachability based on subscriber location and the idiosyncratic ping and traceroute behavior.So — I apologize to Comcast, and I’m quite happy with their willingness to discuss this with me further.