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Advertising Equal Cost Multi- Path (ECMP) Routes in BGP 61 st IETF, Washington DC Manav Bhatia (manav@riverstonenet.com)manav@riverstonenet.com Joel M. Halpern (jhalpern@megisto.com)jhalpern@megisto.com

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Introduction Providers install ECMP routes, announce just one. This can break routing, policies, etc.

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N2 N1 R1 10/8 AS_PATH: X X1 NEXT_HOP N1 AS Y AS X AS Z 10/8 AS_PATH: Z Z1 NEXT_HOP N2 R3 R2 * 10/8 N1 AS X * 10/8 N2 AS Z N3 AS W 10/8 AS_PATH X X1 NEXT_HOP N1 10/8 AS_PATH Z Z1 ECMP_NEXT_HOP N2 10/8 AS_PATH: Y {X Z} {X1 Z1} NEXT_HOP R3 How it works?

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What if R2 and R3 don’t support ECMP extensions? R1 announces the UPDATEs with the following AS_PATH: {X Z} {X1 Z1}

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Constructing Synthetic AS_PATHs AS_PATH1: X Z {A B C} AS_PATH2: X1 Z1 XZ1 AS_PATH: Y Y Y {X X1 Z Z1 A B C XZ1} AS_PATH: {X X1} AS_PATH: Y {X X1} {Z Z1} {A B C XZ1} {Z Z1}{A B C XZ1}

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Constructing Synthetic AS_PATHs - II AS_PATH1: X Z {A B C} AS_PATH2: X1 Z1 {A B C} AS_PATH3: X2 Z2 Z3 AS_PATH: Y Y Y {X X1 X2 Z Z1 Z2 A B C Z3} AS_PATH: {X X1 X2} AS_PATH: Y {X X1 X2} {Z Z1 Z2} {A B C Z3} {Z Z1 Z2}{A B C Z3}

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With BGP ECMP.. Can avoid sub-optimal routing with Route Reflectors Avoid some cases of persistent route oscillations Load Balance BGP!

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How do we deal with.. Multiprotocol Extensions BGP Route Flap Dampening BGP/MPLS VPNs Regular Expressions Splitting load across ASes

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Next Steps Operator Feedback Making it a WG doc

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