Definition
Border Gateway Protocol (BGP) is the standardized exterior gateway protocol that lets independently operated networks, called autonomous systems (AS), tell each other which blocks of IP address space they can reach. It is a path-vector protocol: rather than computing a shortest path by cost like an interior protocol, BGP advertises full AS-path lists and lets each network apply its own policy when choosing a route. Every participating network owns a unique Autonomous System Number (ASN) assigned through the regional registries, and the entire public internet is essentially the sum of these AS-to-AS announcements.
eBGP, iBGP, and route advertisement
When BGP runs between routers in two different autonomous systems it is called external BGP (eBGP); when it carries those learned routes between routers inside one AS it is internal BGP (iBGP). Through peering sessions, routers exchange prefixes (such as 203.0.113.0/24) and the AS-path needed to reach them. BGP then selects a best path using attributes like AS-path length, local preference, and configured policy. Because acceptance is policy-driven, misconfigured or malicious announcements can hijack or black-hole traffic, which is why route filtering and RPKI origin validation matter.
Why it matters for sovereignty
BGP is the layer at which a network becomes truly self-sovereign on the internet. Operating your own ASN and address space, then announcing it via BGP to multiple upstreams, removes dependence on any single provider's IP allocation and is the foundation for running resilient infrastructure or an anycast deployment. For a self-hoster this is the deep end of the pool; most begin with simpler perimeter tools such as a firewall before ever touching the routing table that holds the network together.
In Simple Terms
Border Gateway Protocol (BGP) is the standardized exterior gateway protocol that lets independently operated networks, called autonomous systems (AS), tell each other which blocks of…