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Advertising Equal Cost Multi-Path Routes in BGP

Advertising Equal Cost Multi-Path Routes in BGP. Manav Bhatia Samsung India Software Operations, Bangalore – India July 17, 2003 57 th IETF - Vienna draft-ecmp-routes-in-bgp-00.txt. The Problem Statement. Route Reflectors only reflect the routes which “they” think are the best !

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Advertising Equal Cost Multi-Path Routes in BGP

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  1. Advertising Equal Cost Multi-Path Routes in BGP Manav BhatiaSamsung India Software Operations, Bangalore – IndiaJuly 17, 2003 57th IETF - Vienna draft-ecmp-routes-in-bgp-00.txt

  2. The Problem Statement • Route Reflectors only reflect the routes which “they” think are the best ! • True Load Balancing not always possible • In some cases leads to persistent route Oscillations • Solutions in RFC 3345 place Network Design Constraints which is not a long term solution – Protocol must be enhanced

  3. Route Reflector’s View of the Best Path

  4. Solution

  5. BGP MED Oscillation - 1

  6. BGP MED Oscillation - 2

  7. BGP MED Oscillation - 3

  8. BGP MED Oscillation – The Solution

  9. How to Advertise Multiple BGP Routes? • If more than one route for a given NLRI is announced then it is considered as an implicit withdraw for the former advertisement • New Optional Non Transitive attribute ECMP_NEXT_HOP introduced • NEXT_HOP attribute not mandatory if ECMP_NEXT_HOP present • Semantics of the BGP UPDATE message unchanged • Modify Phase 2 and Phase 3 of the Decision Process

  10. ECMP_NEXT_HOPAttribute

  11. Advertising multiple routes with ECMP_NEXT_HOPattribute

  12. Appending routes using ECMP_NEXT_HOPattribute

  13. Removing one of the Multiple Routes

  14. Pragmatic Considerations • Advertising both Reachable and Unreachable Prefixes • Multi-Protocol BGP • Additional Load in the Network • Impact on BGP Convergence • Flapping BGP ECMP route • May give higher degree of preference to a peer we know has more number of ECMP routes

  15. Next Steps • Possibly combine with draft-lefaucheur-multiprotocol-nh-00.txt • Get Feedback !

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