Internet is inter-network. I have network at my home. My internet service provider (ISP) has their own network. That giant internet searching services has thei

Internet is inter-network. I have network at my home. My internet service provider (ISP) has their own network. That giant internet searching services has their own network. How are they interconnected? BGP (Border Gateway Protocol) is one of routing protocol used by those different networks to connect to each other. Internet formed. Bird is a software that implement BGP. You can run it on a pc instead of buying specific routing device (Cisco, juniper, Mikrotik, etc).