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draft-francois -segment-routing-ti-lfa- 00

draft-francois -segment-routing-ti-lfa- 00. Pierre Francois, IMDEA Networks Institute Clarence Filsfils , Ahmed Bashandy , Cisco Systems Bruno Decraene , Stephane Litkowski , Orange IETF 89, RTGWG WG. Topology Independent Fast Reroute using Segment Routing. Fast Reroute

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draft-francois -segment-routing-ti-lfa- 00

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  1. draft-francois-segment-routing-ti-lfa-00 Pierre Francois, IMDEA Networks Institute Clarence Filsfils, Ahmed Bashandy, Cisco Systems Bruno Decraene, Stephane Litkowski, Orange IETF 89, RTGWG WG

  2. Topology Independent Fast Reroute using Segment Routing • Fast Reroute • Local protection of traffic against sudden failuresof links and nodes • IP-FRR behavior when SR comes into play • Topology Independent coverage • Full coverage for link and node protection • Segment Routing • Leveraging the SR architecture allows to enforce any failover path

  3. Which failover path? • New in IP-FRR: Post-convergence path from the PLR to the destination B C E A D F 100 100 100 100 PE1 PE2 LFA TI-LFA

  4. Why that choice? • Post-convergence path • Typically in line with capacity planning • Easy to predict • SR: No need for TLDP sessions • Useless to favor LFA over RLFA over… • Easier to provide the path that the operators actually want

  5. Exercise • draft-ietf-rtgwg-lfa-manageability-01 • Cases where default IP-FRR behavior is not ideal • Need for manageability to enforce an ideal path • Turns out to always be the post-convergence one… • Common sense • The operator configures metrics to obtain optimum paths for its services (bw, delay, …) • The PLR should respect such objectives upon FRR

  6. How to do TI-LFA • Enforcing loop-freeness on post-convergence path • Where can I release the packet? • At the intersection between the new shortest path and the per-destination Q-Space of the destination • How do I reach the release point? • By chaining intermediate segments that are assessed to be loop-free • Maths: homework • How many segments?

  7. How many segments? • Link protection, symmetric topology: • Maximum 2, guaranteed • Most often, 1 is enough • When a post-convergence LFA is available: 0 • Link protection, asymmetric topology • Many asymmetric nets where 2 was the max • A few cases here and there were a bit more are needed for a couple of links • Node protection • Never more than 4, rarely more than 2 • -01 contains numbers • Eager to increase the number of case studies

  8. Protecting AdjSID’s • Packet with 2 top ADJ SIDs [AD, DF, …] • The packet should go to D • Repair: [C, D, DF, …], oif B B C E A D F

  9. Protecting AdjSID’s • Packet with 1 top ADJ SID [AD, F, …] • Option • The packet could go to D • Repair: [C, D, F, …], oif B • The packet could go directly to F • Repair: [C, F, …], oif B B C E A D F

  10. Summary • FRR for Segment Routing • Node and Adjacency Segments • No more TLDP session required for FRR purposes • Full coverage • More than 2 segments are rarely needed • Post-convergence paths • Better fit with capacity planning • Respect of the ISP policy • 1 implementation available • At least one more on the way

  11. Thank you!

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