Collateral Lesson 3: If You Refuse Someone Peering, You Create a Customer for your Competitor
If ISP “A” refuses to peer with ISP “B,” two possibilities exist:
B will buy transit from one of A’s competitors to reach A, or
B will peer with one of A’s transit providers to reach A.
At best, A loses the possibility of selling B transit, and creates a customer for one of their own competitors.
At worst, A loses the possibility of selling B transit, and has to pay to receive traffic which B can send for free in any volume.