Peer groups and Peer worries

It's a fascinating thing, that the internet really does work as its meant to be. It's even more fascinating when it's not working.
Interconnecting different ISPs or service providers is called peering. This boils down to: You can walk through my garden, if I can walk through yours. More specific: your customers can walk through my garden if mine can walk through yours.
In the internet, it's of course the customers customers customers customers.
And sometimes, major league ISPs don't play along well.
Renesys Blog has some details about an internet outage that affected customers of Telia and Cogent in a way, that the doors between Telia and Cogent had been locked up thoroughly.
As Renesys details: Of course, the list of impacted networks is too long to be included here, but they include a wide range of commercial, educational and government clients. On the Telia side, the victims include the Swedish Defense Data Agency, the Finnish State Computer Center, and broadband customers in St. Petersburg. With regard to Cogent, Blue Cross and Blue Shield of Delaware, Kansas State University and Reuters America were all collateral damage.