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MPLS SDN 2016 - Microloop avoidance with segment routing
The document discusses micro-loops in networks and how segment routing can be used to avoid them. Micro-loops are a natural phenomenon in hop-by-hop routed networks caused by transient disagreements between routers during convergence. Segment routing allows building a temporary loop-free path using a two-stage convergence - first using a precomputed loop-free label stack, then switching to the standard path once convergence is complete. This approach could help address issues caused by micro-loops like broken fast reroute and traffic loss.
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Introduction to micro-loops, phenomena, and effects in hop-by-hop routed networks, specifically MPLS. Discusses causes and impacts on convergence times.
Micro-loops can occur locally or remotely. Discusses how micro-loops impact traffic, causing packet loss over certain link speeds.
Micro-loops disrupt Fast-Reroute (FRR) and lead to significant traffic issues, escalating from 100Mbps to 1Gbps, highlighting the urgency of addressing these concerns.
Explores strategies such as mitigation and avoidance, detailing methods like dropping packets, reducing convergence time, and utilizing local delays.
Current methods to tackle micro-loops have limitations. Suggestions to enhance performance and the need for innovative approaches like Segment Routing.
Discussion on using Segment Routing for creating loop-free paths during convergence, and detailing TI-LFA-like approaches for temporary solutions.
Highlights successful lab tests that demonstrate the effectiveness of Segment Routing in avoiding micro-loops, indicating practical benefits and ease of deployment.
Recap of micro-loops as a significant issue, the benefits of Segment Routing, and thankfulness for the audience and their engagement.
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MPLS SDN 2016 - Microloop avoidance with segment routing
- 1. 1 Orange Restricted Avoidingmicro-loops using Segment Routing Stéphane LITKOWSKI Network Architect, Orange Expert
- 2. 2 Orange Restricted Amicro-loop ? Does my network have loops ? Micro-loops are a natural phenomenon in hop by hop routed networks This applies to MPLS networks ! Caused by a transient disagreement between routers during convergence Good and bad events may create loops Duration of micro-loop depends of convergence time S N1 N2 D 1 101 1
- 3. 3 Orange Restricted Amicro-loop ? Does my network have loops ? Micro-loops are a natural phenomenon in hop by hop routed networks This applies to MPLS networks ! Caused by a transient disagreement between routers during convergence Good and bad events may create loops Duration of micro-loop depends of convergence time S N1 N2 D 1 101 1
- 4. 4 Orange Restricted Amicro-loop ? Does my network have loops ? Micro-loops are a natural phenomenon in hop by hop routed networks This applies to MPLS networks ! Caused by a transient disagreement between routers during convergence Good and bad events may create loops Duration of micro-loop depends of convergence time S N1 N2 D 1 101 1
- 5. 5 Orange Restricted Amicro-loop ? Does my network have loops ? Micro-loops are a natural phenomenon in hop by hop routed networks This applies to MPLS networks ! Caused by a transient disagreement between routers during convergence Good and bad events may create loops Duration of micro-loop depends of convergence time S N1 N2 D 1 101 1
- 6. 6 Orange Restricted Amicro-loop ? Does my network have loops ? Micro-loops are a natural phenomenon in hop by hop routed networks This applies to MPLS networks ! Caused by a transient disagreement between routers during convergence Good and bad events may create loops Duration of micro-loop depends of convergence time S N1 N2 D 1 101 1 ! SLOW !
- 7. 7 Orange Restricted Amicro-loop ? Does my network have loops ? Micro-loops are a natural phenomenon in hop by hop routed networks This applies to MPLS networks ! Caused by a transient disagreement between routers during convergence Good and bad events may create loops Duration of micro-loop depends of convergence time S N1 N2 D 1 101 1 ! SLOW !
- 8. 8 Orange Restricted Amicro-loop ? Does my network have loops ? Micro-loops are a natural phenomenon in hop by hop routed networks This applies to MPLS networks ! Caused by a transient disagreement between routers during convergence Good and bad events may create loops Duration of micro-loop depends of convergence time S N1 N2 D 1 101 1
- 9. 9 Orange Restricted Wheredo micro-loops happen ? Anywhere ! They can be local or remote ! R1 R4 R2 DS 10 111 1 R3 Local loop Remote loop Remote loop
- 10. 10 Orange Restricted Whydo I need to take of micro-loops ? Micro-loops break Fast-reroute ! Micro-loops affect traffic which is not concerned by the topology change ! Traffic between S and N2 suffers of packet loss ! 100Mbps of traffic entering a loop on a 5ms RTD link will become 1Gbps in about 40msec ! S N1 N2 D 1 101 1Traffic Time
- 11. 11 Orange Restricted Whydo I need to take of micro-loops ? Micro-loops break Fast-reroute ! Micro-loops affect traffic which is not concerned by the topology change ! Traffic between S and N2 suffers of packet loss ! 100Mbps of traffic entering a loop on a 5ms RTD link will become 1Gbps in about 40msec ! S N1 N2 D 1 101 1Traffic Time
- 12. 12 Orange Restricted Whydo I need to take of micro-loops ? Micro-loops break Fast-reroute ! Micro-loops affect traffic which is not concerned by the topology change ! Traffic between S and N2 suffers of packet loss ! 100Mbps of traffic entering a loop on a 5ms RTD link will become 1Gbps in about 40msec ! S N1 N2 D 1 101 1Traffic Time
- 13. 13 Orange Restricted Whydo I need to take of micro-loops ? Micro-loops break Fast-reroute ! Micro-loops affect traffic which is not concerned by the topology change ! Traffic between S and N2 suffers of packet loss ! 100Mbps of traffic entering a loop on a 5ms RTD link will become 1Gbps in about 40msec ! S N1 N2 D 1 101 1 FRR ! Traffic Time
- 14. 14 Orange Restricted Whydo I need to take of micro-loops ? Micro-loops break Fast-reroute ! Micro-loops affect traffic which is not concerned by the topology change ! Traffic between S and N2 suffers of packet loss ! 100Mbps of traffic entering a loop on a 5ms RTD link will become 1Gbps in about 40msec ! S N1 N2 D 1 101 1 FRR ! Traffic Time
- 15. 15 Orange Restricted Whydo I need to take of micro-loops ? Micro-loops break Fast-reroute ! Micro-loops affect traffic which is not concerned by the topology change ! Traffic between S and N2 suffers of packet loss ! 100Mbps of traffic entering a loop on a 5ms RTD link will become 1Gbps in about 40msec ! S N1 N2 D 1 101 1 ! SLOW ! FRR ! Traffic Time
- 16. 16 Orange Restricted Whydo I need to take of micro-loops ? Micro-loops break Fast-reroute ! Micro-loops affect traffic which is not concerned by the topology change ! Traffic between S and N2 suffers of packet loss ! 100Mbps of traffic entering a loop on a 5ms RTD link will become 1Gbps in about 40msec ! S N1 N2 D 1 101 1 ! SLOW ! Traffic Time
- 17. 17 Orange Restricted Whydo I need to take of micro-loops ? Micro-loops break Fast-reroute ! Micro-loops affect traffic which is not concerned by the topology change ! Traffic between S and N2 suffers of packet loss ! 100Mbps of traffic entering a loop on a 5ms RTD link will become 1Gbps in about 40msec ! S N1 N2 D 1 101 1Traffic Time
- 18. 18 Orange Restricted Whydo I need to take of micro-loops ? Micro-loops break Fast-reroute ! Micro-loops affect traffic which is not concerned by the topology change ! Traffic between S and N2 suffers of packet loss ! 100Mbps of traffic entering a loop on a 5ms RTD link will become 1Gbps in about 40msec ! S N1 N2 D 1 101 1Traffic Time
- 19. 19 Orange Restricted Whydo I need to take of micro-loops ? Micro-loops break Fast-reroute ! Micro-loops affect traffic which is not concerned by the topology change ! Traffic between S and N2 suffers of packet loss ! 100Mbps of traffic entering a loop on a 5ms RTD link will become 1Gbps in about 40msec ! S N1 N2 D 1 101 1Traffic Time Link congestion !
- 20. 20 Orange Restricted Strategiesto address micro-loop issues Not a new topic ! Look at RFC5715 .. Mitigation • Drop looping packets (not so easy !) • Converge faster (minimize micro-loop duration) Avoidance • Local delay (draft-ietf-rtgwg-uloop-delay) • Ordered FIB (RFC6976) • PLSN (RFC5715) • Incremental metric (INFOCOM 2007 paper from P. Francois, M. Shand, O. Bonaventure) • …
- 21. 22 Orange Restricted Strategiesto avoid micro-loops Local delay = OFIB(1) Upon link down, only local router will delay its convergence Upon link up, local router will delay flooding Solves only local micro-loops Multiple implementations available for link down event S N R1 R2 D N2 I will delay by 1200msec I will delay by 1200msec
- 22. 23 Orange Restricted Conclusionon current state of the art No definitive solution to avoid micro-loops Local delay is good but not perfect Mitigation is not enough and sometimes complex to implement How can we improve ?
- 23. 24 Orange Restricted Whynot using Segment Routing ? Segment Routing can build a loop-free path See my talks in 2014 and 2015 on TI-LFA Why not applying a temporary loop-free path ? Two stages convergence Stage#1 : use loop-free path (timer based) Stage#2 : use standard path S N R1 D N2 10 Node_SID_N2 Adj_SID_N2R1 Payload
- 24. 36 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100
- 25. 37 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Payload
- 26. 38 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Payload
- 27. 39 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Payload
- 28. 40 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Payload
- 29. 41 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Payload Stage#1 : tunnel {Adj-SID_R2-D}
- 30. 42 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Stage#1 : tunnel {Adj-SID_R2-D} Payload Adj- SID_R2-D
- 31. 43 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Stage#1 : tunnel {Adj-SID_R2-D} Payload Adj- SID_R2-D Stage#1 : tunnel {Node_SID_R2;Adj-SID_R2-D}
- 32. 44 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Stage#1 : tunnel {Adj-SID_R2-D} Payload Adj- SID_R2-D Stage#1 : tunnel {Node_SID_R2;Adj-SID_R2-D} Stage#1 : tunnel {forward to D}
- 33. 45 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Payload Stage#1 : tunnel {Node_SID_R2;Adj-SID_R2-D} Stage#1 : tunnel {forward to D} Stage#2 : normal FIB update
- 34. 46 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Payload Stage#1 : tunnel {forward to D} Stage#2 : normal FIB update Stage#2 : normal FIB update
- 35. 47 Orange Restricted Multipleapproaches possible to build a loop-free path One is TI-LFA-like approach Upon link failure, we can compute a loop-free label stack to the destination (as in TI-LFA) The loop-free path will be kept for a time waiting for the other to convergence All the routers applies this two stages convergence R1S DR2 10 R4 100 Payload Stage#2 : normal FIB update Stage#2 : normal FIB update Stage#2 : normal FIB update
- 36. 48 Orange Restricted Dreamor reality ? Technology is a reality ! And we already tested it ! R2R1S R3 R4 R5 R6 10 10 S,R1,R2 are Cisco XR nodes with early code R3,R4,R5,R6 are non Cisco In the setup, SPF delays have been highly increased to make the microloop phenomenon more visible
- 37. 49 Orange Restricted Labevaluation : S-R1 link failure Without micro-loop avoidance FRR Micro-loop effect WITH micro-loop avoidance (LOCAL- DELAY) FRR ! LOOP AVOIDED ! FRR ! LOOP AVOIDED ! WITH micro-loop avoidance (SR)
- 38. 50 Orange Restricted Labevaluation : R2-R4 link failure Without micro-loop avoidance Micro-loop effect WITH micro-loop avoidance (LOCAL- DELAY) Micro-loop effect !!! LOOP NOT AVOIDED !!! FRR WITH micro-loop avoidance (SR) ! LOOP AVOIDED !
- 39. 51 Orange Restricted Segmentrouting micro-loop avoidance Early code testing shown very good results Works for multiple traffic types (IP, MPLS LDP, SR) The technology brings a high benefit in avoiding micro-loops Local mechanism : no protocol extension no interoperability required (expect support of SR) Incremental deployment with incremental benefit
- 40. 52 Orange Restricted Conclusion Micro-loopsare a real issue Current solutions are not satisfying (complex or limited) Segment routing helps in creating temporary loop-free path Two stages convergence remains the GOOD idea ! SR micro-loop avoidance works ! : see demo from Cisco at their booth
- 41.