> This is how all the big CDNs do it

You have no idea how big CDNs do it. I've personally installed CDN gear into ISP racks. Sometimes you get an uplink into a router, other times you sit on a switch with other gear.

That "direct fiber interconnect" is called private peering and mostly used to fill cache boxes on the providers network.

I spent a year in 2007-2008 managing equipment inside Comcast's network while working for a very much not-Comcast company. Even had a Comcast VPN assigned specifically to me complete with RSA fob shipped to me by Comcast. You haven't got the first clue what ISPs do, nor how networks work.

> No; no ISP would ever run externally managed equipment inside their network.

You haven't been paying attention to that Edward Snowden fella, have you?

Just stating the obvious here, but "Rule #1" obviously doesn't apply to service provider networks, who are specifically built so other people's equipment can be connected on almost every point. Customers on the access layer. Datacenters, colocation and these sorts of boxes on the distribution layer, and peers on the "gateway"/peering layers.

The second paragraph is wrong too, there are much closer relationships possible. They're much deeper than that today, and I would expect in the future to see CDNs much deeper in provider networks.