MPLS SDN 2016 - Microloop avoidance with segment routing

1. 1 Orange Restricted Avoiding micro-loops using Segment Routing Stéphane LITKOWSKI Network Architect, Orange Expert

2. 2 Orange Restricted A micro-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 A micro-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 A micro-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 !

9. 9 Orange Restricted Where do 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 Why do 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 Why do 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 Why do 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 Why do 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 Why do 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

19. 19 Orange Restricted Why do 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 Strategies to 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 Strategies to 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 Conclusion on 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 Why not 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 Multiple approaches 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 Multiple approaches 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 Multiple approaches 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 Multiple approaches 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 Multiple approaches 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 Multiple approaches 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 Multiple approaches 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 Multiple approaches 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 Multiple approaches 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 Dream or 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 Lab evaluation : 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 Lab evaluation : 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 Segment routing 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-loops are 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. 53 Orange Restricted Thank you

MPLS SDN 2016 - Microloop avoidance with segment routing

MPLS SDN 2016 - Microloop avoidance with segment routing

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