[collinmanderson]

My guess is because it does cost some money to do local peering. My understanding is you need to contact each individual company you want to peer with, make sure you both have a Point of Presence in the same datacenter, sign a contract, etc. So you both need to be renting space in that building and both have an open port on your router, and then you need to pay the datacenter to actually physically run the wire between the routers.

[mirimir]

Thanks. I hadn't thought it through so clearly.

But wait, how does traffic get to that remote peer?

[collinmanderson]

> how does traffic get to that remote peer?

Not sure what you mean. The two networks (say, a DSL and Cable provider in the same area), need to physically connect at some location in the area (usually at a "Carrier Hotel"). Once they're connected, traffic originating from a DSL customer is routed through the DSL network to the Carrier Hotel, then across the to the Cable provider's network, and then through that Cable network to the Cable customer.

For example, I live in South Bend, IN, where we have Comcast Cable and AT&T DSL. Although we have a few places in town where Comcast and AT&T _could_ each have a point of presence, and then peer with each other, they don't think that's worth it. Instead, traffic is routed to the nearest peering point, which in my case is 350 E Cermak in Chicago, 100 miles away. Peering locally would probably save about 10ms, but that's probably not really worth it.

[mirimir]

OK, I get it. In your example, AT&T and Comcast peer in Chicago. In my example, the two Icelandic ASNs peered near Amsterdam. Likely through international intermediaries.