Topology Independent LFA Orange use case & applicability

Stéphane Litkowski, Orange Expert

Bruno Decraene, Orange Expert

MPLS 2014

2 TI-LFA

Orange Business Service

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One of the largest dedicated network for business • Worldwide :

• 172 countries, 900+ cities • France :

• more than 2 million business clients, SMBs and companies in France

IP VPN

Ethernet

Internet

Cloud

Voice & Telepresence

High value: availability, security,

SLA

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Agenda

Requirements

Topology Independent LFA

Applicability on Orange topologies

Simulation results

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Agenda

Requirements

Topology Independent LFA

Applicability on Orange topologies

Simulation results

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Why using Fast Reroute ?

Applications are more and more sensitive (VoIP, CRM, Sync, transport)

Customers do not want to rewrite or customize their applications code to handle network failures

Fast convergence is below 1sec BUT:

– hard to have the same performance on all nodes

– hard to maintain convergence time while network is growing

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FRR issue Primary path Backup path

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South East

8ms

5ms

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Backup 8ms

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FRR issue

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FRR 33ms

Primary path 5ms

FRR

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How to improve ?

Requirements

– 100% coverage link and node protection

– No transient congestion

– Optimal routing

– Simple solution to operate and understand

– Scalable solution

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What is the more optimal and natural path upon a failure ?

Post-convergence path from the PLR

Benefits of using Postconvergence path :

– Policy compliant and optimized

– Well sized

– Well known

D

S Potential backup Path

Postconvergence Path How to use Post-convergence path for FRR ?

How to improve ?

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Agenda

Requirements

Topology Independent LFA

Applicability on Orange topologies

Simulation results

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Segment Routing

Segment Routing technology may use any path without any need of signalling

Allows to use « unlimited » number of paths

Let’s simply compute Post Convergence Path and enforce it to be loopfree using SR

R1

R6

R5

R2

R3

R4

D

S SR Segments

IP

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Topology Independent LFA :

– Segment Routing Fast-Reroute solution

– Providing 100% coverage (node/link/SRLG)

– encoding any FRR path by using Segment Routing blocks :

– any Service Provider policy (LFA policy framework)

– including post-convergence path as new criteria

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Topology Independent LFA

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Topology Independent LFA

Cannot use a strict only Explicit Path due to depth of segment stack

We need to compress the stack

Done by reusing rLFA/dLFA building blocks (P & Q space)

S R1 R2 R3 D

R4 R5 R6

MPLS MPLS MPLS MPLS

2

MPLS

AdjR5

AdjR6

AdjR3

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AdjR6

AdjR3

MPLS

AdjR3

MPLS

Primary

EPC FRR

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Topology Independent LFA

FRR path is computed as follows :

– Compute postconvergence shortest path (new SPF)

– Enforce loop-freeness by :

– finding a P node on the path

– finding a Q node on the path after P (P and Q may be equal)

– Only P to Q path would be explicit and may be additionnaly compressed using nodal segments

S R1 R2 R3 D

R4 R5 R6

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2

MPLS

NodeR5

MPLS

NodeR5

MPLS

MPLS

PQ

S R1 R2 R3 D

R4 R5 R6

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2

MPLS

NodeR5

MPLS MPLS

MPLS

P 50

Q

AdjR6

NodeR5

AdjR6 AdjR6

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Topology Independent LFA

Computation complexity is manageable :

– P-Space comes from old Primary SPT

– Q-Space needs one rSPT per nexthop

– New primary SPT per local failure (link or node)

Expected depth of FRR stack :

– Only 2 segments at max for link protection in symetric networks

– There is always a P adjacent to a Q

– A bit more for some node protection cases but we can add a second level of compression (by running new fSPFs)

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Agenda

Requirements

Topology Independent LFA

Applicability on Orange topologies

Simulation results

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Analysis on topologies : case #1 TI-LFA for path optimality

Paris Paris

Paris Paris STR

STR

Dijon

Lyon

Lyon

Paris

Lyon

Poitiers

Primary

Backup

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Paris

Out of transit node

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Analysis on topologies : case #1 TI-LFA for path optimality

Paris Paris

Paris Paris STR

STR

Dijon

Lyon

Lyon

Paris

Lyon

Poitiers

LFA

MRT

FRR path

RSVP-TE link protection (1:n)

Paris

Out of transit node

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Analysis on topologies : case #1 TI-LFA for path optimality

Paris1

Paris2

Paris3

Paris5

STR

STR

Dijon

Lyon

Lyon

Paris4

Lyon

Poitiers

EPC FRR

Nodal

EPC stack composed of one segment

Protection stack

Node_Paris4

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Paris

Out of transit node

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Analysis on topologies : case #2 TI-LFA vs LFA/rLFA

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PE1

P1

PE2

P2

P5 P4

P3

PE3

40

15

10k 10k

20

20

20

30

39

Primary

Backup

10k

LFA : • PE2 is defacto node

protection (not guaranteed) rLFA : • cannot guarantee node

protection

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Analysis on topologies : case #2 TI-LFA vs LFA/rLFA

SR segment

EPC provides node protection with 1 segment

Protection stack

Node_P3

Backup

PQ

PE1

P1

PE2

P2

P5 P4

P3

PE3

40

15

10k 10k

20

20

20

30

39

10k

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Analysis on topologies : case #3 TI-LFA using multiple segments

PE1

R1

PE2

R2 R3

R4 R5

R6

R7

PE3

1

7

3

3

3 1

1 1

1 1

2

100 100

Primary

Backup

SR Segments

Nodal to PE3

Protection stack compressed

Node_R3

Node_PE3

P

Q Protection stack (PQ)

Adj_R3

Adj_R4

Adj_R6

Adj_R7

Adj_PE3

Top

Bottom

Top

Bottom

Nodal to R3

Nodal to PE3

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Analysis on topologies : case #4 Maximum observed stack depth

PE1

PE2

R1

R2

R3

R4

R5 R6

100

100

2 1

2

3

3

1

3

1 3

1000

P

Q Protection stack (PQ)

Node_R3

Adj_R4

Adj_R5

Adj_R6

Adj_PE2

Protection stack compressed

Node_R5

Node_R6

Node_R3

Adj_PE2

Primary

Backup

SR Segments

Top

Bottom Top

Bottom

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Agenda

Requirements

Topology Independent LFA

Applicability on Orange topologies

Simulation results

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Simulations results on 11 Orange Networks Depth of protection stack

11 topologies have been analyzed including multiple network types and size

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Simulations results on 11 Orange Networks Per node analysis (node protection case)

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92% of nodes from ALL topologies have 99% of its repair_lists with a size <=2

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Simulations results on 11 Orange Networks

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80% of nodes have 12 or less distinct repair_lists

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Simulations results on 11 Orange Networks Path compression : computation complexity

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100% FRR link/node protection is a requirement

Current FRR technics may cause some side effects :

– Transient network congestion

– Additionnal management for selection of the backup path

Topology Independent LFA :

– Scalable : no additional state in the network

– Simple to compute

– Provides 100% link/node protection

– Prevents any side effect by using a well sized and optimal path

– Simple to understand : well known path

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Conclusion

Thank you !