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Exploring BGP: An Overview of Border Gateway Protocol

Dive into the BGP environment, understand how BGP works, its administration, routing policies, and decision processes. Learn about BGP data structures, routing information sources, and the importance of network scalability in the modern internet.

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Exploring BGP: An Overview of Border Gateway Protocol

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  1. Border Gateway ProtocolBGP-4 • BGP environment • How BGP works • BGP information • BGP administration

  2. Routing and Routers • IGP (internal gateway protocols) • Distance vector protocols • Link state protocols • EGP (external gateway protocols • BGP (boarder gateway protocol) • First version BGP 1 (1989) • Current standard de facto (1993)

  3. BGP - Requirements • No restriction on the network deployment • Scalability • Loop-free routing • Manageable routing policy • CIDR support

  4. CIDR Format Networks represented by tuple <prefix(IP), length(bit)> E.G. <198.24.160.0, 19> represents 198.24.160.0 255.255.224.0 1100110.00011000.10100000.00000000 1111111.11111111.11100000.00000000 --------19 bit -------

  5. BGP Environment Autonomous system (AS) definition • Single technical administration • Single routing policy • Unique identifying number

  6. AS Topology • Stub AS • Multihomed AS • Transit • Non transit

  7. How BGP Works ? • Using TCP (port 179) as a transport layer • Establish connection • Establish BGP session • Data base export / import • Incremental updates • Decision process

  8. Information Sources • EGP • IGP • Dynamic • Semi-dynamic • Static routes

  9. BGP Data Base • Input table (incoming routes) • Local routing table <-> IP forwarding table • Output table

  10. BGP Update Structure • Withdrawn list • Path attribute • Network layer Reachability information (NLRI)

  11. Route Information(The Path Attribute) • NEXT_HOP • AS_PATH • Local preference • MULTI_EXIT_DISC • Origin • Community • Atomic aggregation • Aggregator

  12. BGP Decision Process • Next hop is inaccessible • Largest local preference • Locally originated path • Shortest AS_PATH • IGP before EGP • Lowest MED • Shortest internal path (IGP) • Lowest router ID

  13. Administrator Intervention (Policy) • Identify route (match) • Filtering (accept \ reject) • Manipulate attributes (action) • Local preference • As path

  14. AS_PATH Manipulation

  15. Topology restriction Scalability Loop-free routing CIDR Manageable Segregation to ASs Support the current internet deployment The path attribute BGP syntax Static routes, Filtering policy, attribute manipulation Conclusion

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