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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 ! - PowerPoint PPT Presentation
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Advertising Equal Cost Multi-Path Routes in BGP
Manav BhatiaSamsung India Software Operations,Bangalore – IndiaJuly 17, 200357th IETF - Viennadraft-ecmp-routes-in-bgp-00.txt
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
Route Reflector’s View of the Best Path
IGP Cloud
AS X
AS Y
Route Reflector
Rclient 2
R3
Rclient 1
3
3
BGP Information BGP Peering IGP Connection
Solution
IGP Cloud
AS X
AS Y
Route Reflector
Rclient 2
R3
Rclient 1
3
3
BGP Information BGP Peering IGP Connection BGP Information usingECMP_NEXT_HOP
BGP MED Oscillation - 1
AS Y
BGP Information
IBGP Peering EBGP Peering
AS Z
AS X
MED Low(M2)MED Hi
(M3)MED Low
(M1)
Router IDR2
Router IDR1
High IGPCost (C2)
Low IGPCost (C1)
RouteReflector
Client
(Non)Client
AS Z, MED M3,
RID R1
AS Z,MED M2
BGP MED Oscillation - 2
AS Y
Advertised BGPInformation
IBGP Peering EBGP Peering
AS Z
AS X
MED Hi(M3)
MED Low(M1)
Router IDR2
Router IDR1
High IGPCost (C2)
Low IGPCost (C1)
RouteReflector
Client
(Non)Client
AS Z,MED M2
AS Z,MED M2
BGP MED Oscillation - 3
AS Y
Advertised BGPInformation
IBGP Peering EBGP Peering
AS Z
AS X
MED Hi(M3)
MED Low(M1)
Router IDR2
Router IDR1
High IGPCost (C2)
Low IGPCost (C1)
RouteReflector
Client
(Non)Client
AS Z,MED M2
AS Z,MED M2
Withdrawn BGPInformation
AS Y,MED M1,
R2
BGP MED Oscillation – The Solution
AS Y
BGP Information
IBGP Peering EBGP Peering
AS Z
AS X
MED Low(M2)MED Hi
(M3)MED Low
(M1)
Router IDR2
Router IDR1
High IGPCost (C2)
Low IGPCost (C1)
RouteReflector
Client
(Non)Client
AS Z, MED M3,
RID R1 AS Z,MED M2
BGP Information advertisedusing ECMP_NEXT_HOP
AS Y, MED M1,
RID R2
Z C2M2
ASIGPCost
MED
Z C1M3
Y C1M1
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
ECMP_NEXT_HOP AttributeAddress Family Identifier (2 Octets)
Number of Next Hops (1 Octet)
Length of the First Next Hop (1 Octet)
Network Address of the First Next Hop (Variable)
. . .
Length of the second Next Hop (1 Octet)
Network Address of the second Next Hop (Variable)
Length of the “n” Next Hop (1 Octet)
Network Address of the “n” Next Hop (Variable)
Advertising multiple routes with ECMP_NEXT_HOP attribute
AS PATH 100 101
NEXT_HOP 23.42.21.2
MED 56
AS PATH 500 601
NEXT_HOP 4.14.13.11
MED 56
AS PATH 100 101
NEXT_HOP 3.1.1.132
MED 56
AS PATH 100 101
NEXT_HOP 34.13.15.3
MED 56
AS PATH 100 101
NEXT_HOP 3.1.1.132
MED 56
FamilyAF_INET
Number of Next Hops2
Length of 1st Next Hop4
Network Address34.13.15.3
Length of 2nd Next Hop4
Network Address23.42.21.2
ECMP_NEXT_HOP
Withdrawn Routes Length0
BGP_UPDATE
10.0.0.0/8
ECMP_NEXT_HOPAttribute
Appending routes using ECMP_NEXT_HOP attribute
AS PATH 100 101
NEXT_HOP 23.42.21.2
MED 56
AS PATH 500 601
NEXT_HOP 4.14.13.11
MED 56
AS PATH 100 101
NEXT_HOP 3.1.1.132
MED 56
AS PATH 100 101
NEXT_HOP 34.13.15.3
MED 56
AS PATH 500 601
MED 56
FamilyAF_INET
Number of Next Hops1
Length of 1st Next Hop4
Network Address4.14.13.11
ECMP_NEXT_HOP
Withdrawn Routes Length0
BGP_UPDATE
ECMP_NEXT_HOPAttribute
10.0.0.0/8
Removing one of the Multiple Routes
AS PATH 100 101
NEXT_HOP 23.42.21.2
MED 56
AS PATH 500 601
NEXT_HOP 4.14.13.11
MED 56
AS PATH 100 101
NEXT_HOP 3.1.1.132
MED 56
AS PATH 100 101
NEXT_HOP 34.13.15.3
MED 56
AS PATH 100 101
MED 56
FamilyAF_INET
Number of Next Hops1
Length of 1st Next Hop4
Network Address3.1.1.132
ECMP_NEXT_HOP
Withdrawn Routes10.0.0.0/8
BGP_UPDATE
ECMP_NEXT_HOPAttribute
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
Next Steps Possibly combine with draft-lefaucheur-
multiprotocol-nh-00.txt Get Feedback !
