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SR-MPLS Update - DKNOG Clarence Filsfils Cisco Fellow

Industry backs up SR Multi-vendor Consensus with strong customer adoption in SP, DC, Metro, and Enterprise networks. Standardization in IETF for de-facto SDN architecture. Enhanced OAM and PerfMon, micro-loop avoidance, and 5G three-tiered latency service. SR-TE and Flex-Algo for delay optimization. SR-PCE and binding segments for seamless deployment and automated steering. MPLS/SDN 2015 talk on Segment Routing and source routing. Available on Amazon.

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SR-MPLS Update - DKNOG Clarence Filsfils Cisco Fellow

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  1. SR-MPLS Update - DKNOG Clarence Filsfils Cisco Fellow – cf@cisco.com

  2. Industry at large backs up SR Multi-vendor Consensus • Open Source • Linux, VPP Strong customer adoption WEB, SP, DC, Metro, Enterprise Standardization IETF De-facto SDN Architecture

  3. SR Unified Fabric Attributes Seamless Deployment Inter Domain On-Demand SR policy & Automated Steering Stateless Service Chain Automated 50ms Protection Enhanced OAM & PerfMon Micro-Loop Avoidance

  4. 5G three-tiered latency serviceSR-TE and Flex-Algo delay bound = 15 3 1 2 min-delay 4 6 5 Min Cost

  5. Part II is available! amzn.com/B01I58LSUO amazon.com/dp/B07N13RDM9

  6. ReminderMPLS/SDN 2015 talk

  7. Segment Routing • Source Routing • the source chooses a path and encodes it in the packet header as an ordered list of segments • the rest of the network executes the encoded instructions without any further per-flow state • Segment: in MPLS, a label

  8. IGP Prefix Segment • Shortest-path to the IGP prefix • Global • 16000 + Index • Signaled by ISIS/OSPF

  9. IGP Adjacency Segment • Forward on the IGP adjacency • Local • 1XY • X is the “from” • Y is the “to” • Signaled by ISIS/OSPF

  10. BGP Peering Segment • Forward to the BGP peer • Local • 1XY • X is the “from” • Y is the “to” • Signaled by BGP-LS (topology information) to the controller

  11. SR PCE SR PCE • SR PCE collects via BGP-LS • IGP segments • BGP segments • Topology BGP-LS BGP-LS 5 7 4 6 2 BGP-LS Low Lat, Low BW 14 13 12 11 3 1 10 PEER DC (BGP-SR) WAN (IGP-SR)

  12. An end-to-end path as a list of segments SR PCE • SR-PCE computes that the green path can be encoded as • 16001 • 16002 • 124 • 147 • SR-PCE programs a single per-flow state to create an application-engineered end-to-end policy Low-Latency to 7for application … 7 6 4 2 5 Low Lat, Low BW 50 {16001, 16002, 124, 147} 13 12 11 10 3 1 14 Default ISIS cost metric: 10 PEER DC (BGP-SR) WAN (IGP-SR)

  13. Binding Segment SR PCE PCEP-request (SR Policy, low-latency, to 4) • SR-PCE instructs edge to install an SRTE policy • For this traffic, push this list of segments • The edge router assigns a binding segment to the SRTE policy and installs it in dataplane • Pop and Push the related list of segments • Binding segment is local • Controller collects binding segments and characteristics of the SRTE policies (e.g. PCEP) PCEP-reply (OK, BSID: 200) 2 4 6 5 50 200: pop and push {16002, 124} 3 1 Default ISIS cost metric: 10Default Latency metric: 10 WAN

  14. An end-to-end path with binding segment SR PCE • SR-PCE computes that the green path can be encoded as • 16001 • 200 • 147 Low-Latency to 7for application … 5 7 4 2 6 Low Lat, Low BW 50 Push{16001,200, 147} 13 12 11 10 3 1 14 Default ISIS cost metric: 10Default Latency metric: 10 PEER PEER DC (or AGG) WAN

  15. Segment Routing • Inter-domain Policy • Undelivered service prior to SR • Stateless • RSVP-TE lays state in n^2*k • Scale • Simplification • No LDP, no RSVP-TE • Automation • TI-LFA, SR native algorithm, SR-PCE

  16. Per-Link Delay Measurement

  17. Link Delay – Probe Measurement • One Way Delay = (T2 – T1) • Two-Way Delay = ((T2 – T1) + (T4 – T3)) / 2 • Timestamps added in hardware • PM Query message using RFC 6374 packet format with MPLS/GAL or IP/UDP Encap performance-measurement interface GigE0/0/0/0 delay-measurement performance-measurement interface GigE0/0/0/0 delay-measurement RX Timestamp T2 TX Timestamp T1 PM Query Packet 1 2 Local-end Remote-end PM Response Packet TX Timestamp T3 RX Timestamp T4 Default: every 3 sec

  18. Per measurement interval • Probe every 3sec • Over a measurement interval (default 30sec) • minimum • average • maximum • variance

  19. SRTE handles Minimum delay (propagation delay) • Minimum delay provides the propagation delay • fiber length / speed of light • A property of the topology • with awareness of DWDM circuit change • SRTE (Policy or Flex-Algo) can optimize on min delay

  20. QoS handles Average, Max and Variance (buffer) • Depends on buffer congestion • (traffic burst over line rate) / line rate • Highly variable at any time scale • Not controlled by routing optimization • Controller by QoS • Priority queue, WRR, WFQ… • Tail-Drop, RED…

  21. Routing stability – Telemetry accuracy Every 30sec (10 queries) EDT Telemetry push 1 2 Every 120sec IF significant min changeTHEN trigger an ISIS/OSPF flood ISIS/OSPF/BGP-LS update

  22. ISIS, OSPF, and BGP-LS signaling • Advertise extended TE metrics – e.g. link delay (in usec) • Unidirectional Link Delay • Minimum and Maximum Unidirectional Link Delay • Unidirectional Link Delay Variation • RFC 7810 (IS-IS) • RFC 7471 (OSPF) • draft-ietf-idr-te-pm-bgp (BGP-LS)

  23. IGP SR Flex-Algo for min delay Leveraged by SRTE • SR Policy for min delay router isis 1 flex-algo 128 metric-type delay segment-routing traffic-eng policy FOO color 20 end-point ipv4 1.1.1.3 candidate-paths preference 100 dynamic metric type delay

  24. Per-Policy Delay Measurement

  25. Configuration SR Policy 2 4 1 5 Headend Endpoint D:100 D:100 Default ISIS metric: 10 Default ISIS delay (D): 10 3 segment-routing traffic-eng policy FOO color 20 end-point ipv4 1.1.1.5 delay-measurement candidate-paths preference 100 dynamic metric type delay

  26. Probe Measurement • One Way Delay = (T2 – T1) • Requires clock synchronization • Default: Send Query every 3 sec • PM packets same format as link delay measurement RX Timestamp T2 TX Timestamp T1 PM Query Packet In SR Policy SR Policy 2 4 1 5 Headend Endpoint 3 PM out-of-bandResponse Packet

  27. Telemetry • Use telemetry to collect the evolution of the end-to-end delay metrics at fine time scale (min, max, avg at probe period) • In first release, no routing reaction to excess measured latency Every 30sec (10 queries) EDT Telemetry push 2 4 1 5 3

  28. SR IGP Flex-Algo

  29. Flexible Algorithm • We call “Flex-Algo” • An algorithm defined by the operator, on a per-deployment basis • Flex-Algo K is defined as • The minimization of a specified metric: IGP, TE or delay • The exclusion of certain link properties: affinity or SRLG • Example • Operator1 defines Flex-Algo 128 as “minimize IGP metric and avoid link-affinity “green” • Operator2 defines Flex-Algo 128 as “minimize delay metric and avoid link-affinity “blue”

  30. Flex-Algo Participation and Prefix-SID • Each node MUST advertise the Flex-Algo(s) that it participates in • A Flex-Algo K can be enabled on all or a subset of nodes • Each node can participate in multiple Flex-Algos • Likely it also advertises prefix SIDs for these Flex-Algos

  31. Example: 3 planes: 0 / 128 / 129 • All nodes support standard Algo 0 • Green nodes advertise support for Flex-Algo 128 as “Minimize IGP metric” • Red nodes advertise support for Flex-Algo 129 as “Minimize IGP metric” • Each node k advertises a Prefix SID for every Algo it supports: • 1600k for Algo 0 • 1680k for Algo 128 • 1690k for Algo 129 16002 Algo 0 1 2 16802 Flex-Algo 128 Alg128 4 3 0 • 16009 Algo 0 9 16809 Flex-Algo 128 6 5 Alg129 • 16909 Flex-Algo 129 7 8 16007 Algo 0 • 16907 Flex-Algo 129

  32. No additional loopback address • Flex-Algo Prefix SIDs can be advertised as additional prefix-SIDs of the existing loopback address 1 2 4 3 1.0.0.9/32 • 16009 Algo 0 • 16809 Flex-Algo 128 • 16909 Flex-Algo 129 0 9 6 5 7 8

  33. Flex-Algo Definition • Each node MUST have the definition of the Flex-Algo(s) that it is participating in • e.g. Flex-Algo 128: minimize on IGP metric and avoid TE affinity RED • Local configuration • likely automated via a solution such as NSO • Learned from a central entity via ISIS flooding • new top TLV defined for Flex-Algo definition advertisement Algo 128: minimize IGP metric Algo 129: minimize IGP metric

  34. Computation • A node N computes Flex-Algo K if • it is enabled for K, and • it has a consistent definition for K • If so, the first step is to define the topology of K • N prunes any node that is not advertising participation to K • N prunes any link that is excluded by the algorithm of K • e.g. if K excludes TE-affinity RED then any link with TE-affinity RED is pruned • The resulting topology is called Topo(K) • The second step is to compute shortest-path tree on Topo(K) with the metric defined by K • it could be the IGP metric, the TE metric or the delay

  35. FIB installation • The third step is to install any reachable Prefix-SID of Flex-Algo K in the forwarding table along the computed shortest-path on Topo(K)

  36. Summing up the config 16002 Algo 0 16802 Flex-Algo 128 • Grey nodes support Algo 0/128/129 • Green nodes support 0/128 • Red nodes support 0/129 • Algo 128: minimize IGP metric • Algo 129: minimize IGP metric • Each node K advertises a Prefix SID for every Algo it supports: • E.g. 1600K for Algo 01680K for Algo 1281690K for Algo 129 1 2 Alg128 4 3 0 • 16009 Algo 0 9 16809 Flex-Algo 128 6 5 • 16909 Flex-Algo 129 7 8 Alg129 16007 Algo 0 • 16907 Flex-Algo 129

  37. Topo(0) 1 2 4 3 0 9 6 5 7 8

  38. Topo(128) 1 2 Alg128 4 3 0 9

  39. Topo(129) 0 9 6 5 7 8 Alg129

  40. Prefix-SID 16009 of Algo 0 1 2 4 3 0 9 6 5 7 8

  41. Prefix-SID 16809 of Flex-Algo 128 1 2 4 3 0 9

  42. Prefix-SID 16909 of Flex-Algo 129 0 9 6 5 7 8

  43. TI-LFA • The TI-LFA algorithm is performed within Topo(K) • The backup path is expressed with Prefix-SIDs of Algo K • Benefits: the backup path is optimized per Flex-Algo!

  44. ODN and AS Inter-Domain delay 2/8 via 9 with min delay 2/8 via 9 with min-delay • Any node of both domain supports Algo 128 • Algo 128 is defined as min-delay • The delay of each link is reported in drawing BGPRR 23 9 3 1 2 2 2 1 1 1 2/8 9 0 16 7 2 2 4 5 6 Domain 1 Domain 2 • The IGP metric per link is 10 • 9 advertises 2/8 with color 100

  45. ODN and AS Inter-Domain delay – Cont. SR PCE 1: Min-delay to 9? • Upon receiving 2/8, node 0 dynamically creates an SR Policy to 9 • As 9 is beyond its domain, node 0 requests the computation from its PCE • PCE replies with MPLS stack <16805, 16809>, leveraging the Flex-Algo(128) SIDs 2: <16805, 16809> FIB 2/8: push <16805, 16809> 23 9 Algo 128:16809 3 1 2 2 2 1 1 1 2/8 9 Algo 128:16805 0 16 7 2 2 4 5 6 16809 16805

  46. Cumulative-Metric Bound

  47. 3-tiered latency service • Minimum Latency • ISIS Flex-Algo 128  minimize the delay to the endpoint • Minimum Cost • ISIS Algo 0  minimize the isis metric to the endpoint

  48. 3-tiered latency service • Minimum Latency • ISIS Flex-Algo 128  minimize the delay to the endpoint • Minimum Cost • ISIS Algo 0  minimize the isis metric to the endpoint • Minimum Cost but with a bound on the delay • SRTE Policy • SR Native Algorithm • Minimize IGP metric • Cumulative delay along the path <= delay bound Another obvious business service that was never realized before SR

  49. Business Relevance: Cost vs Latency • Core • Cheaper • Longer delay • Access Shortcut • Most expensive • Lowest latency • Metro Shortcut • In-between Access Metro Core 3 1 2 4 6 5

  50. Bulk of the traffic - Best-Effort 3 1 2 4 6 5 Min igp metric

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