Routing Resiliency Latest Enhancements

Transcription

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2 Routing Resiliency Latest Enhancements Clarence Filsfils

3 Agenda Per-Prefix LFA Remote LFA Segment Routing Topology-Independent LFA 3

4 Acknowledgement Stephane Litkowski and Bruno Decraene, Orange 4

5 Per-Prefix LFA

6 Per-Prefix LFA C D1 C is an LFA for D1 if CD1 < CS + SD1 S E F D2 IGP pre-computes a backup path per primary path to an IGP destination FIB pre-installs the backup path in dataplane Upon local failure, all the backup paths of the impacted destinations are enabled in a prefix-independent manner (<50msec LoC) Hierarchical HW FIB organization Similar to BGP-PIC FRR behavior 6

7 Benefits Simple Sub-50msec Link, Node and SRLG Protection Deployment friendly no protocol change, no interop testing, incremental deployment Good Scaling No degradation on IGP convergence for primary paths 7

8 Constraints Coverage is topology dependent availability of a backup path depends on topology In some rare cases, there are multiple LFA candidates and the one taken might not be the best choice 8

9 LFA Coverage is in fact excellent 11 real Core Topologies average coverage: 94% of destinations 5 topologies higher than 98% coverage Real Aggregation simple design rules help ensure 100% link/node protection coverage for most frequent real aggregation topologies RFC6571 Sweet Spot A simple solution is essential for access/aggregation as it represents 90% of the network size hence complexity 9

10 High interest for access/aggregation Is there a way to also support the ring and biased square? Ring Biased Square (a<c) 10

11 One backup path per primary path Default tie-break 1. Prefer primary over secondary 2. Prefer lowest backup path metric 3. Prefer linecard disjointness 4. Prefer node disjointness CLI to customize the tie-break policy Default is recommended. Simplicity. 11

12 Primary vs Secondary S has two primary paths to D E1 and E2 S has one LFA candidate to D: N1 Which backup to prefer? Another primary path or a secondary path? N1 S E1 F D E2 N1 E1 S F D E2 N2 12

13 Guaranteed-Node-Protecting Definition: ND < NF + FD (Eq2) does the path from the neighbor to D avoid node F? S s primary path to D: E0 S s LFA candidates: E1 and E2 E1: not guaranteed node protecting N1 does not meet Eq2 E2: guaranteed node protecting N2 meets Eq2 N1 E1 S E0 F D E2 20 N2 13

14 De Facto Node Protection E0 S F D E N2 Choosing a guaranteed node-protecting LFA is not the only way to benefit from LFA node protection A non-guaranteed node protecting LFA candidate might turn to be node protecting. We call this De Facto Node Protection N2 is not guaranteed node protecting for D: 20!< But if F fails, N2 will trigger its own LFA for the path N2FD (via N2D) and hence the traffic SD avoids F! 14

15 Lowest backup path metric S s primary path to D: F Two LFA Candidates: N1 and N2 Lowest backup path metric: N2 SN2 + N2D < SN1 + N1D < S F D E1 E2 E0 N1 N

16 Still in some cases, the LFA is suboptimal 16

17 Remote LFA

18 Remote-LFA Objective Keep Per-prefix LFA benefits simplicity incremental deployment Increase coverage for real topologies primarily for ring and biased-square access topologies potentially for core topology 98/99% is seen as good-enough 100% coverage is icing on the cake 18

19 The Ring No LFA protection in the ring if E4 sends a C1-destined packet to E3, E3 sends it back to E4 19

20 PQ Algorithm Any node which meets the P and Q properties P: the set of nodes reachable from E4 without traversing E4E5 Q: the set of nodes which can reach E5 without traversing E4E5 Best PQ node the closest from A: E1 Establish a directed LDP session with the selected PQ node E5 E4 Backbone C1 C2 E3 Access Region E1 E2 20

21 Remote LFA Protection E4 s LIB E5 s label for FEC C2 = 20 E3 s label for FEC E1 = 99 E1 s label for FEC C2 = 21 E4 s FIB for destination C2 Primary: out-label = 20, oif = E5 Backup: out-label = 21 oif = [push 99, oif = E3] E5 E4 C E3 21 C2 E1 E2 RLFA is LFA from a remote node (E1) With Node and SRLG protection! 21

22 Remote LFA applied in the backbone PQ s coverage extension is significant for some SP s 22

23 Targeted LDP - Scalable Odd ring: 2 LDP additional sessions per node Even ring: 1 LDP additional session per node 23

24 Targeted LDP - Scalable Small number of automatically signaled LDP sessions per node 24

25 Very simple rules RFC6571 In a square, any metric should be less than the sum of the 3 other links Simple rule: any link in a square should have a metric less than the sum of the 3 other links E1 can send a C2-destined packet to E2 whatever the E1E2 metric, but E2 forwards it to C2 only if E2C2 is < E2E1C1C2 C2 sends a C1-bound packet to C1 only if C2C1 < C2E2E1C1. Applying this for any link in the square we see that a link metric should be less than the sum of the other 3 link metrics 25

26 Not yet 100%-guaranteed E1 has no LFA for C1 E2 routes back E1 has no RemoteLFA for C1 P and Q intersection is null 26

27 100% - Icing on the cake When the P and Q space do not intersect, then setup an Explicit-Path-LSP to the closest Q node use SR explicit path! See next. Automated 100% guarantee Node protection 27

28 Remote LFA Benefits Seamless integration with Per-Prefix LFA Packets take their shortest paths from the PQ node Destinations use per-prefix LFA onto physical oif when available (i.e. perprefix LFA), and per-prefix LFA onto LDP LSP (i.e. Remote LFA) otherwise Simple Automated computation, negligible CPU, low TLDP requirement Incremental Deployment New code only at the protecting node Meet the real coverage requirements backbone and access/aggreation 28

29 Segment Routing

30 Segment Routing : the source chooses a path and encodes it in the packet header as an ordered list of segments : an identifier for any type of instruction Service Context Locator IGP-based forwarding construct BGP-based forwarding construct Local value or Global Index 30

31 Segment Routing : an ordered list of segments is represented as a stack of labels a completed segment is popped : an ordered list of segments is represented as a routing extension header, see 4.4 of RFC2460 Type 0 could be used. A new type is proposed to enhance functionality while improving forwarding performance and security upon completion of a segment, the pointer is incremented 31

32 ISIS automatically installs segments Nodal segment to C A B C D Nodal segment to C Adj Segment Z M N O P Simple extension Excellent Scale: a node installs N+A FIB entries N node segments and A adjacency segments Nodal segment to Z 32

33 Node Segment Packet to Z FEC Z push 65 A B C 65 Packet to Z swap 65 to Packet to Z swap 65 to 65 pop Packet to Z D Packet to Z Z 65 A packet injected anywhere with top segment 65 will reach Z via shortest-path Z advertises a global node segment 65 with its loopback simple ISIS sub-tlv extension we assume the same SRGB at every node All remote nodes install in their FIB the node segment 65 to Z 33

34 Adjacency Segment A B C M N O Pop 9003 D P Z A packet injected at node C with segment 9003 is forced through datalink CO C allocates a local segment 9003 and maps it to the instruction complete the segment and forward along the interface CO C advertises the adjacency segment in ISIS simple sub-tlv extension C is the only node to install the adjacency segment in FIB 34

35 Combining Segments ECMP Node segment Per-flow state only at head-end not at midpoints Source Routing the path state is in the packet header Packet to Z Packet to Z Packet to Z 72 A B C M N O Packet to Z 78 D P 65 Packet to Z Z 65 Packet to Z 35

36 Simple and Efficient Transport of MPLS services PE1 A M All VPN services ride on the node segment to PE2 B N Efficient packet networks leverage ecmp-aware shortest-path! node segment! Simplicity no complex LDP/ISIS synchronization to troubleshoot one less protocol to operate PE2 IPv4 over MPLS/IGP VPN over MPLS/IGP Internet over MPLS/IGP PW over MPLS/IGP IPv6 over MPLS/IGP 36

37 Topology Independent LFA (TI-LFA) Guaranteed Link/Node FRR in any topology even with asymmetric metrics No Directed LDP session Simplicity entirely automated (no need for customization) Incremental deployment Applicable to LDP and IP primary traffic Only the repair tunnel is SR-based For networks with symmetric metric & link protection No extra computation Simple repair stack Node segment to P node Adjacency segment from P to Q Demo available E1 C1 Backbone E2 Node segment to P node E3 C2 Default metric: 10 E Adj segment to Q node 37

38 Central OptimizationN Need 2Gbps from A to Z with SLA Collect network status information Encoded path for traffic to Z {66, 9001, 65} 66 Congested A B C D 9001 M N O P Z 65 ABCOPZ meets SLA. I account the BW. I encode the path as nodal segment to C, adj segment to O, nodal segment to Z Centralized Optimization - find a path meeting the SLA requirement - encode it as a list of nodal and adjacent segments Agility and Scalability Hybrid Central/Distributed CP 38

39 Many other use-cases See 39

40 Topology-Independent LFA

41 Benefits 100%-coverage 50-msec link and node protection Simple to operate and understand automatically computed by the IGP Prevents transient congestion and suboptimal routing leverages the post-convergence path, planned to carry the traffic Incremental deployment applicable to primary IP and LDP traffic only the repair tunnel needs to be SR-enabled Demo available 41

42 Explicit Post-Convergence Path What is the more optimal and natural path upon a failure? the post-convergence path Why have we never used it before SR? the post-convergence path may not be an LFA and hence may loop Thanks to SR, we can always use the post-convergence path Explicit Post-Convergence (EPC): the non-lfa portion of the path is encoded as an explicit list of segments 42

43 Explicit Post-Convergence Path Computation leverages proven and existing LFA technology intersection of post-convergence SPT with P and Q spaces Number of Segments to form the Repair Tunnel Symmetric network, link protection: Proven: <= 2 segments to get into Q space Asymmetric network or node protection: No theoretical bound In reality, as we already saw for RLFA, things are much simpler! Orange use-case 100% link protection 100% use <= 2 segments 100% node protection (<=4 segments) 99.72% use <= 2 segments 0.24% use 3 segments 0.04% use 4 segments 43

44 FRR Path Optimality 44

45 45

46 Conclusion

47 Segment Routing Wide Applicability Simple to deploy and operate More scalable and functional IP and MPLS Agile Wan Orchestration with hybrid centralized/distributed Massive operator interest and support ISIS/SR demonstrated in Feb 2013 TI-LFA demonstrated in Oct 2013 Much more happening! Join the community. 47

48 TI-LFA Applicable to native IP, LDP and SR traffic does not require a migration from LDP to SR Incremental deployment does not require an overall SR deployment 100% coverage link, node and SRLG 100% automated fit the post-convergence path 48

49 Thank you

50 References Per-prefix LFA Applicability: RFC 6571 Remote LFA: draft-ietf-rtgwg-remote-lfa-04 Topology-Independent LFA: draft-francois-segment-routing-ti-lfa-00 50

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