Border Gateway Protocol (BGP) is a protocol that enables ISPs and NSPs to exchange routing information among themselves. BGP is used to determine the best path for sending data packets across the Internet. BGP is also known as the protocol of the Internet backbone, as it connects different autonomous systems (ASes) that form the Internet. BGP is not used by end systems or local networks, but only by routers that operate at the border of ASes. BGP is a complex and dynamic protocol that can handle changes in network topology, traffic load, and policy requirements. BGP is also a scalable protocol that can support the growth of the Internet1234 Reference:
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2: 1.8: Internet Backbones, NAPs, and ISPs - cs.huji.ac.il
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4: Border Gateway Protocol - Wikipedia