BGP

Problem

The Internet is not one network. It's thousands of independently controlled networks: ISPs, cloud providers, companies, universities, governments. Your network knows: 142.250.x.x is not here. But: Which other network should I send the packet to? There is no single router controlling the Internet.

Solution — BGP

Networks tell neighboring networks: “I can reach these IP prefixes.”

Google
   ↓
 ISP B
   ↓
 ISP A
   ↓
  You
ISP B can tell ISP A:

142.250.0.0/15 is reachable through me. BGP distributes this reachability while allowing every independently controlled network to apply its own routing policy.

Core idea: BGP lets independent networks exchange reachability while retaining control over their routing decisions.