Thanks for the responses to my query.
Here's what happened to my network.
On 3/17/2010 in the morning Central Time in Houston we started having issues
connecting to parts of the rest of the world on an intermittent basis. We
were troubleshooting our own equipment for quite some time and did not
realize that Cogent was having routing/peering issues with Time Warner
(Telecom?). Apparently it was an issue that was supposed to have started
3/17/2010 at 9:00am Central Time and effected Houston and Dallas, Texas, USA
and stopped around 1:00pm CT on the same day.
But my experience was that the outage was not resolved until 3/18/2010 at
3:00pm CT (or so).
The Cogent ticket # on the issue was HD2113436.