Configure BGP Confederation & Fake Confederation in Bird (Updated 2020-06-07)

Changelog 2020-10-01: Add warning to not filter private ASNs within the internal network 2020-06-07: Add limitations of Bird confederation and a way to simulate confederation 2020-05-17: Initial version Comparison of BGP Interconnection Schemes within an ISP Most ISPs, or Internet Service Providers, use the BGP protocol to exchange their route information. Each ISP will obtain an ASN (Autonomous System Number) from the regional NIC (Network Information Center, e.g., APNIC, RIPE), like China Telecom's ASN is 4134 for example. Then, ISPs connect their boundary routers via physical links (copper line, fiber, satellite link, etc.), and configure BGP protocol on the boundary routers, so they will tell the other part that: "I'm AS4134, and I can provide access to the IP block of 202.101.0....