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Apparently there is a peering dispute between Cogent (AS174) and Telia (AS1299). This has caused a partition between their networks, such that Cogent and Telia customers can’t talk to each other directly. As expected, the Renesys blog provides good coverage of this situation.

The only aspect of the Renesys analysis that I’m uncertain about is whether Cogent actively did something (in addition to depeering) to block Telia’s routes. Renesys says that the Telia prefixes showed up in Cogent’s tables, and vice versa, via several other tier-1’s such as Verizon, Level(3), AT&T and others for about 12 hours after the depeering. On the surface this suggests that at least one of Cogent or Telia has (paid) transit relationships with those tier-1’s. But when I look at Level(3)’s looking glass I see prefixes from both Cogent and Telia with the Level3_Peer community. Closer to home, looking at routes via the Savvis (AS3561) looking glass as well as the policy documented at whois -h rr.savvis.net AS3561 it is obvious that both Cogent and Telia are peers, not transit customers.

So, maybe all those tier-1 networks that provided transit between Cogent and Telia for 12 hours had mis-configured filters. Or maybe they intentionally provided transit between these two peers out of altruistic feelings towards the Internet community. But I doubt both of these possibilities. My guess about Telia or Cogent being a transit customer doesn’t make sense either. I don’t see how anybody could have moved from customer to peer with multiple tier-1 networks in <12 hours. So what happened during those 12 hours? I don’t have nearly the access to data that Renesys has, so I expect that I’m wrong in questioning this. But I just don’t see how this works out.