There have been some reports that Sprint and Cogent are having a bit of a problem.
Seems they are in a tiff about the peering agreement. Sprint has since removed their peering from Cogent.
This basically means, traffic to/from sprint and cogent need to find a different way to route between them. This effects anyone down stream as well. Meaning, if you have a internet link from Sprint, and try to get to someone on Cogent's network - you may not be able too.
This would all hinge on whether or not they have peering agreements with others that allow them to route the other networks - which may not exist since they already had peering.
This is gonna cause some internet instability for some users.