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IP LFA (Loop-Free-Alternative): Architecand TroubleshootingBRKRST-3020

Luc De Ghein

Technical Leader Services

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2014 Cisco and/or its affiliates. All rights reserved.BRKRST-3020 Cisco Public

Agenda

Introduction

LFA Overview

LFA Architecture

Per-link vs per-prefix

Repair path selection and tie-breakers

Remote LFA

Repair path in data plane

Configuration, implementation and troubleshooting (OSPF, ISIS, EIOS and IOS-XR

Conclusion

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Introduction

8/10/2019 Cisco Live IP LFA Architecture and Troubleshooting

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Introduction

Best-effort traffic delivery for IPv4/v6 was good enough

Service failures caused by routing transitions are largely hidden byprotocols that retransmit the lost data

But, this not good enough anymore for voice and video traffic

We need something better: IP-FRR

Low-hanging fruit

MPLS is not needed

One implementation is LFA

IPv4 is used throughout the presentationsame principles apply t

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Goal - Benefits

Provide FAST restoration of traffic flow in case of network failure

Designed to give the same speed of recovery as MPLS TE FRR

Does not require MPLS to function (though may protect MPLS traffic if pres

Remote LFA does require MPLS at this time

The goal was to provide 50 ms restoration (actual speed depends on platfo

Protect

One single link failure

One single node failure

No path protection

Multiple failure conditions are not covered

Simpler than MPLS TE FRR to configure and operate

Good scalability

Incremental deploymentno inter-router signaling specific to LFA FRR

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LFA Overview

8/10/2019 Cisco Live IP LFA Architecture and Troubleshooting

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Convergence, Protection, Restoration

Convergence

In case of failure, the routing protocol computes new best path New best path gets installed in data plane

Fast convergence

Same as above, but faster

Tuned routing protocol

Pre-computed backup path

For speed: pre-computed backup/repair path needed, in data plane

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