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Border Gateway Protocol BGP-4

Border Gateway Protocol BGP-4. BGP environment How BGP works BGP information BGP administration. Routing and Routers. IGP (internal gateway protocols) Distance vector protocols Link state protocols EGP (external gateway protocols BGP (boarder gateway protocol)

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Border Gateway Protocol BGP-4

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 BGP Update Structure • Withdrawn list • Path attribute • Network layer Reachability information (NLRI)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