1. 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

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_HOP Attribute

11. Advertising multiple routes with ECMP_NEXT_HOP attribute

12. Appending routes using ECMP_NEXT_HOP attribute

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 !