The Border Gateway Protocol (BGP) is the core routing protocol of the Internet. It works by maintaining a table of IP networks or "prefixes" which designate network reachability among autonomous systems. BGP makes routing decisions based on path, network policies and/or rulesets.
BGP was created to replace the EGP routing protocol to allow fully decentralized routing in order to allow the removal of the NSFNet Internet backbone network. This allowed the Internet to become a truly decentralized system. Since 1994, version four of the protocol has been in use on the Internet. All previous versions are now obsolete. Most Internet users do not use BGP directly. However, since most Internet service providers must use BGP to establish routing between one another, it is one of the most important protocols of the Internet.
Routers use the Border Gateway Protocol (BGP) to swap information about routes and which ISP has been allocated particular blocks of IP addresses. However, BGP is not secure, and it is possible for a rogue ISP (or one that has been misled by a fraudulent customer) to “announce” someone else’s addresses and thereby reroute traffic.
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