Introduction to Segment Routing

Transcription

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2 Introduction to Segment Routing Michael Kowal, Vertical Solutions

3 Abstract Introduction to Segment Routing This session provides an overview of the segment routing technology and its use cases. This new routing paradigm provides high operational simplicity and maximum network scalability and flexibility. You will get an understanding of the basic concepts behind the technology and its wide applicability ranging from simple transport for MPLS services, disjoint routing, traffic engineering and its benefits in the context of software defined networking. Previous knowledge of IP routing and MPLS is required. 3

4 Agenda Technology Overview Use Cases A Closer Look at the Control and Data Planes Traffic Protection Traffic Engineering Conclusion

5 Technology Overview

6 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 Segment: an identifier for any type of instruction forwarding or service 6

7 Segment Routing Forwarding Plane MPLS: an ordered list of segments is represented as a stack of labels IPv6: an ordered list of segments is encoded in a routing extension header This presentation: MPLS data plane 7

8 IGP Prefix Segment Shortest-path to the IGP prefix Global Index Signaled by ISIS/OSPF DC (BGP-SR) WAN (IGP-SR) PEER 8

9 IGP Adjacency Segment Forward on the IGP adjacency Local 1XY X is the from Y is the to Signaled by ISIS/OSPF DC (BGP-SR) WAN (IGP-SR) PEER 9

10 BGP Prefix Segment Shortest-path to the BGP prefix Global Index Signaled by BGP DC (BGP-SR) WAN (IGP-SR) PEER 10

11 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 Low Lat, Low BW High Lat, High BW DC (BGP-SR) WAN (IGP-SR) PEER 11

12 WAN Controller SR PCE collects via BGP-LS IGP segments BGP segments Topology BGP-LS SR PCE BGP-LS BGP-LS Low Lat, Low BW DC (BGP-SR) WAN (IGP-SR) PEER 12

13 An end-to-end path as a list of segments SR PCE computes that the green path can be encoded as SR PCE programs a single per-flow state to create an applicationengineered end-toend policy 12 {16001, 16002, 124, 147} PCEP, Netconf, BGP DC (BGP-SR) SR PCE Default ISIS cost metric: 10 WAN (IGP-SR) Low Lat, Low BW 7 PEER 13

14 Segment Routing Standardization IETF standardization in SPRING working group Protocol extensions progressing in multiple groups IS-IS OSPF PCE IDR 6MAN Broad vendor and customer support Sample IETF Documents Problem Statement and Requirements (RFC 7855) Segment Routing Architecture (draft-ietf-spring-segment-routing) IPv6 SPRING Use Cases (draft-ietf-spring-ipv6-use-cases) Segment Routing with MPLS data plane (draft-ietf-spring-segment-routing-mpls) Topology Independent Fast Reroute using Segment Routing (draft-francois-rtgwg-segment-routing-ti-lfa) IS-IS Extensions for Segment Routing (draft-ietf-isis-segment-routing-extensions) OSPF Extensions for Segment Routing (draft-ietf-ospf-segment-routing-extensions) PCEP Extensions for Segment Routing (draft-ietf-pce-segment-routing) Close to 40 IETF drafts in progress 14

15 Segment Routing Product Support Platforms: IOS-XR (ASR9000, CRS-1/CRS-3) IOS-XE (ASR1000, CSR1000v, ASR902, ASR903, ISR4400) NX-OS (N3K, N9K) WAN Automation Engine (WAE) SR Traffic Engineering Integration with NSO Upcoming NCS5000, NCS

16 Use Cases

17 IPv4/6 VPN/Service transport IGP only No LDP, no RSVP-TE ECMP vpn pkt 2 3 vpn pkt pkt pkt 6 5 Site Site2 vpn pkt 17

18 Simplest migration: LDP to SR Initial state: All nodes run LDP, not SR LDP LDP LDP 1 LDP 3 4 LDP LDP LDP LDP Domain 18

19 Simplest migration: LDP to SR Initial state: All nodes run LDP, not SR Step1: All nodes are upgraded to SR In no particular order Default label imposition preference = LDP SR+LDP 1 LDP SR+LDP SR+LDP 3 4 SR+LDP SR+LDP SR+LDP SR+LDP Domain 19

20 Simplest migration: LDP to SR Initial state: All nodes run LDP, not SR Step1: All nodes are upgraded to SR In no particular order leave default LDP label imposition preference Step2: All PEs are configured to prefer SR label imposition In no particular order SR+LDP 1 SR segment-routing mpls sr-prefer SR+LDP SR+LDP SR+LDP SR+LDP 2 SR+LDP Domain 20

21 Simplest migration LDP to SR Initial state: All nodes run LDP, not SR Step1: All nodes are upgraded to SR In no particular order leave default LDP label imposition preference Step2: All PEs are configured to prefer SR label imposition In no particular order SR 1 SR SR SR SR 2 Step3: LDP is removed from the nodes in the network In no particular order SR SR SR Domain Final state: All nodes run SR, not LDP 21

22 Seamless Interworking with LDP Seamless Deployment vpn pkt LDP(7) 2 3 vpn pkt vpn pkt pkt pkt 6 5 Site Site2 vpn pkt 22

23 Topology-Independent LFA (TI-LFA FRR) 50msec FRR in any topology IGP Automated No LDP, no RSVP-TE Optimum Post-convergence path No midpoint backup state pkt Detailed operator report S. Litkowski, B. Decraene, Orange pkt Mate Design How many backup segments Capacity analysis pkt 23

24 Automated Traffic Matrix Collection Traffic Matrix is fundamental for capacity planning centralized traffic engineering IP/Optical optimization Most operators do not have an accurate traffic matrix With SR, the traffic matrix collection is automated

25 Optimized Content Delivery On a per-content, per-user basis, the content delivery application can engineer the path within the AS the selected border router the selected peer AS7 5 AS5 7 6 AS6 Also applicable for engineering egress traffic from DC to peer BGP Prefix and Peering Segments pkt AS1 25

26 Application Engineered Routing Per-application flow engineering End-to-End DC, WAN, AGG, PEER Millions of flows No signaling No midpoint state No reclassification at boundaries Low-Latency to 7 for application A12 12 Push {16001, 200, 147} 13 NSO 10 Low-Lat to : pop and push {16002, 16004} SR PCE BSID: 200 ISIS: PeerSID: 147, Low Lat, Low BW PeerSID: 147, High Lat, High BW Low Lat, Low BW DC (or AGG) Default ISIS cost metric: 10 Default Latency metric: 10 WAN PEER 26

27 Application Engineered Routing Per-application flow engineering End-to-End DC, WAN, AGG, PEER Millions of flows No signaling No midpoint state No reclassification at boundaries Low-Latency to 7, DC Plane 0 only, for application A12 12 Push {16010, 16001, 200, 147} 13 NSO 10 Low-Lat to : pop and push {16002, 16004} SR PCE BSID: 200 ISIS: PeerSID: 147, Low Lat, Low BW PeerSID: 147, High Lat, High BW Low Lat, Low BW DC (or AGG) Default ISIS cost metric: 10 Default Latency metric: 10 WAN PEER 27

28 A Closer Look at the Control and Data Planes

29 MPLS Control and Forwarding Operation with Segment Routing Services PE1 MP-BGP PE2 IPv4 IPv6 IPv4 VPN IPv6 VPN VPWS VPLS No changes to control or forwarding plane Packet Transport PE1 IGP PE2 LDP RSVP BGP Static IS-IS OSPF MPLS Forwarding IGP label distribution for IPv4 and IPv6. Forwarding plane remains the same 29

30 SID Encoding Prefix SID SID encoded as an index Index represents an offset from SRGB base Index globally unique SRGB may vary across LSRs SRGB (base and range) advertised with router capabilities Adjacency SID SID encoded as absolute (i.e. not indexed) value Locally significant Automatically allocated for each adjacency SR-enabled Node SRGB = [ ]. Advertised as base = 16,000, range = 7,999 Prefix SID = Advertised as Prefix SID Index = 41 Adjacency SID = Advertised as Adjacency SID =

31 SR IS-IS Control Plane Overview IPv4 and IPv6 control plane Level 1, level 2 and multi-level routing Prefix Segment ID (Prefix-SID) for host prefixes on loopback interfaces Adjacency SIDs for adjacencies Prefix-to-SID mapping advertisements (mapping server) MPLS penultimate hop popping (PHP) and explicit-null label signaling 31

32 Configuring Segment Routing for IPv4 Using IS-IS (Cisco IOS-XR) router isis DEFAULT net address-family ipv4 unicast metric-style wide segment-routing mpls interface Loopback0 passive address-family ipv4 unicast interface GigabitEthernet0/0/0/0 point-to-point address-family ipv4 unicast Enable Segment Routing for IPv4 with MPLS data plane 32

33 SR OSPF Control Plane Overview OSPFv2 control plane Multi-area IPv4 Prefix Segment ID (Prefix-SID) for host prefixes on loopback interfaces Adjacency SIDs for adjacencies MPLS penultimate hop popping (PHP) and explicit-null label signaling 33

34 Configuring Segment Routing for IPv4 Using OSPF (Cisco IOS-XR) router ospf DEFAULT router-id segment-routing mpls segment-routing forwarding mpls area 0 interface Loopback0 passive interface GigabitEthernet0/0/0/0 network point-to-point Enable Segment Routing with MPLS data plane 34

35 MPLS Data Plane Operation Prefix SID SRGB [16,000 23,999 ] Adjacency SID SRGB [16,000 23,999 ] Swap Pop Adjacency SID = X X X X Y Y Payload Payload Payload Payload Packet forwarded along IGP shortest path (ECMP) Swap operation performed on input label Same top label if same/similar SRGB PHP if signaled by egress LSR Packet forwarded along IGP adjacency Pop operation performed on input label Top labels will likely differ Penultimate hop always pops last adjacency SID 35

36 MPLS Data Plane Operation (Prefix SID) SRGB [16,000 23,999 ] SRGB [16,000 23,999 ] SRGB [16,000 23,999 ] SRGB [16,000 23,999 ] A B C D Loopback X.X.X.X Prefix SID Index = 41 Push Push Swap Pop Pop VPN Label VPN Label VPN Label Payload Payload Payload Payload Payload 36

37 MPLS Data Plane Operation (Adjacency SIDs) SRGB [16,000 23,999 ] SRGB [16,000 23,999 ] SRGB [16,000 23,999 ] SRGB [16,000 23,999 ] A B X D Adjacency SID = 126 Loopback X.X.X.X Prefix SID Index = 41 Push Push Push 126 Pop Pop Pop VPN Label VPN Label VPN Label Payload Payload Payload Payload Payload 37

38 MPLS LFIB with Segment Routing LFIB populated by IGP (ISIS / OSPF) PE PE PE PE Forwarding table remains constant (Nodes + Adjacencies) regardless of number of paths PE PE P PE PE Other protocols (LDP, RSVP, BGP) can still program LFIB Network Node Segment Ids Node Adjacency Segment Ids In Label Out Label Out Interface L1 L1 Intf1 L2 L2 Intf1 L8 L8 Intf4 L9 L9 Intf2 L10 Pop Intf2 Ln Pop Intf5 Forwarding table remains constant 38

39 Traffic Protection

40 Topology Independent LFA (TI-LFA) 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 also protects LDP traffic 40

41 Topology Independent LFA Implementation Leverages existing and proven LFA technology P space: set of nodes reachable from node S (PLR) without using protected link L Q space: set of nodes that can reach destination D without using protected link L Enforcing loop-freeness on post-convergence path Where can I release the packet? At the intersection between the post-convergence shortest path and the Q space How do I reach the release point? By chaining intermediate segments that are assessed to be loop-free 41

42 TI-LFA Zero-Segment Example TI-LFA for link R1R2 on R1 Calculate LFA(s) Packet to Z A Z Packet to Z Calculate post-convergence SPT R1 R2 Find LFA on post-convergence SPT R1 will steer the traffic towards LFA R5 prefix-sid(z) Packet to Z 1000 R5 R4 R3 Default metric:10 42

43 TI-LFA Single-Segment Example TI-LFA for link R1R2 on R1 Calculate P and Q spaces They overlap in this case Packet to Z A R1 Z R2 Packet to Z Calculate post-convergence SPT P-space Find PQ node on postconvergence SPT prefix-sid(r4) prefix-sid(z) Packet to Z R5 prefix-sid(z) Packet to Z R1 will push the prefix-sid of R4 on the backup path R4 R3 Q-space Default metric:10 43

44 TI-LFA Double-Segment Example TI-LFA for link R1R2 on R1 Calculate P and Q spaces Packet to Z A Z Packet to Z Calculate post-convergence SPT R1 R2 Find Q and adjacent P node on post-convergence SPT R1 will push the prefix-sid of R4 and the adj-sid of R4-R3 link on the backup path prefix-sid(r4) adj-sid(r4-r3) prefix-sid(z) Packet to Z P-space adj-sid(r4-r3) prefix-sid(z) R5 R Default metric:10 R3 Q-space prefix-sid(z) Packet to Z Packet to Z 44

45 Traffic Engineering

46 Traffic Engineering with Segment Routing Provides explicit routing Supports constraint-based routing Supports centralized admission control No RSVP-TE to establish LSPs Uses existing ISIS / OSPF extensions to advertise link attributes Supports ECMP Segment Routing TE LSP 46

47 How Traffic Engineering Works Head end Mid-point TE LSP IP/MPLS Tail end Link information Distribution ISIS-TE OSPF-TE Path Calculation Path Setup Forwarding Traffic down path Auto-route (announce / destinations) Static route PBR PBTS / CBTS Forwarding Adjacency Pseudowire Tunnel select 47

48 Stateful PCE PCE maintains topology and path database (established paths) More optimal centralized path computation Enables centralized path initiation and update control Well suited for SDN deployments PCC PCEP Stateful PCE LSP DB TED 48

49 Topology Acquisition An external PCE requires some form of topology acquisition A PCE may learn topology using BGP- LS, IGP, SNMP, etc. BGP-LS characteristics aggregates topology across one or more domains provides familiar operational model New BGP-LS attribute TLVs for SR IGP: links, nodes, prefixes BGP: peer node, peer adjacency, peer set PCE BGP-LS Domain 0 RR BGP-LS BGP-LS Domain 1 Domain 2 TED 49

50 Active Stateful PCE PCC or PCE may initiate path setup PCC may delegate update control to PCE PCC may revoke delegation PCE may return delegation PCE has update control over delegated paths PCEP Active Stateful PCE LSP DB TED Stateful PCC 50

51 Active Stateful PCE PCE-Initiated and PCC-Initiated LSPs PCE-Initiated (Active Stateful PCE) PCC-Initiated (Active Stateful PCE) PCE initiates LSP and maintains update control PCEP LSP DB TED PCC initiates LSP and delegates update control PCEP LSP DB TED Stateful PCC Stateful PCC PCE part of controller architecture managing full path life cycle Tighter integration with application demands PCC may initiate path setup based on distributed network state Can be used in conjunction with PCEinitiated paths 51

52 PCE Extensions for Segment Routing (SR) Segment routing enables source routing based on segment ids distributed by IGP PCE specifies path as list of segment ids PCC forwards traffic by pushing segment id list on packets No path signaling required Minimal forwarding state Maximum network forwarding virtualization The state is no longer in the network but in the packet Paths may be PCE- or PCC-initiated PCEP Segment List:: 10,20,30,40 Stateful PCC Node SID Adjacency SID Application Stateful PCE Path Request In Out Int L1 L1 Intf1 L7 L7 Int3 L8 Pop Intf3 L9 Pop Intf5 LSP DB TED Forwarding table remains constant 52

53 Conclusion

54 Conclusion Simple routing extensions to implement source routing Packet path determined by prepended segment identifiers (one or more) Data plane agnostic (MPLS, IPv6) Network scalability and agility by reducing network state and simplifying control plane Traffic protection with 100% coverage with more optimal routing Recommended Follow-up Session: Segment Routing: Technology and Use-cases (BRKRST-3122) 54

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57 Segment Routing Sessions Cisco Live 2016 Introduction to Segment Routing () Segment Routing: Technology and Use-cases (BRKRST-3122) Application Engineered Routing: Allowing Applications to Program the Network (BRKSPG-2066) Segment Routing in Datacenter using Nexus 9000/3000 (BRKDCN-2050) Cisco WAN Automation Engine (WAE) Network Programmability with SR (LTRMPL-2104) Segment Routing in Datacenter using Nexus 9000/3000 (LABRST-2020) Next Generation Service Provider Network using Segment Routing & BIER (LABSPG-2012) DevNet Workshop Application Engineered Egress Routing (DEVNET-2062) DevNet Workshop Enabling Containers to Leverage SR (DEVNET-2063) 57

58 Continue Your Education Demos in the Cisco campus Walk-in Self-Paced Labs Table Topics Meet the Engineer 1:1 meetings Related sessions 58

59 Please join us for the Service Provider Innovation Talk featuring: Yvette Kanouff Senior Vice President and General Manager, SP Business Joe Cozzolino Senior Vice President, Cisco Services Thursday, July 14 th, :30 am - 12:30 pm, In the Oceanside A room What to expect from this innovation talk Insights on market trends and forecasts Preview of key technologies and capabilities Innovative demonstrations of the latest and greatest products Better understanding of how Cisco can help you succeed Register to attend the session live now or watch the broadcast on cisco.com

60 Backup Slides

61 IS-IS Configuration Required Wide metrics SR enabled under unicast address family Optional Prefix-SID configured under loopback(s) AF IPv4 MPLS forwarding enabled automatically on all (non-passive) IS-IS interfaces Adjacency-SIDs are automatically allocated for each adjacency 61

62 Configuring Segment Routing for IPv4 Using IS-IS (Cisco IOS XR) router isis DEFAULT net address-family ipv4 unicast metric-style wide segment-routing mpls interface Loopback0 passive address-family ipv4 unicast prefix-sid absolute interface GigabitEthernet0/0/0/0 point-to-point address-family ipv4 unicast Enable Segment Routing for IPv4 with MPLS data plane Advertise prefix SID (index 41) for Loopback0 62

63 Configuring Segment Routing for IPv6 Using IS-IS (Cisco IOS XR) router isis DEFAULT net address-family ipv6 unicast metric-style wide segment-routing mpls interface Loopback0 passive address-family ipv6 unicast prefix-sid absolute interface GigabitEthernet0/0/0/0 point-to-point address-family ipv6 unicast Enable Segment Routing for IPv6 with MPLS data plane Advertise prefix SID (index 61) for Loopback0 63

64 OSPF Configuration OSPFv2 control plane Required Enable segment-routing under instance or area(s) Command has area scope, usual inheritance applies Enable segment-routing forwarding under instance, area(s) or interface(s) Command has interface scope, usual inheritance applies Optional Prefix-SID configured under loopback(s) MPLS forwarding enabled on all OSPF interfaces with segment-routing forwarding configured 64

65 Configuring Segment Routing for IPv4 Using OSPF (Cisco IOS XR) router ospf DEFAULT router-id segment-routing mpls segment-routing forwarding mpls area 0 interface Loopback0 passive prefix-sid absolute interface GigabitEthernet0/0/0/0 network point-to-point Enable Segment Routing with MPLS data plane Advertise prefix SID (index 41) for Loopback0 65

66 Configuring Topology Independent Fast Reroute for IPv4 using Segment Routing and IS-IS (Cisco IOS XR) router isis DEFAULT net address-family ipv4 unicast metric-style wide segment-routing mpls interface Loopback0 passive address-family ipv4 unicast prefix-sid absolute interface GigabitEthernet0/0/0/0 address-family ipv4 unicast fast-reroute per-prefix fast-reroute per-prefix ti-lfa Enable TI-LFA for IPv4 prefixes on interface GigabitEthernet0/0/0/0 66

67 Configuring Topology Independent Fast Reroute for IPv6 using Segment Routing and IS-IS (Cisco IOS XR) router isis DEFAULT net address-family ipv6 unicast metric-style wide segment-routing mpls interface Loopback0 passive address-family ipv6 unicast prefix-sid absolute interface GigabitEthernet0/0/0/0 address-family ipv6 unicast fast-reroute per-prefix fast-reroute per-prefix ti-lfa Enable TI-LFA for IPv6 prefixes on interface GigabitEthernet0/0/0/0 67

68 Configuring a Mapping Server for SR and LDP Interworking for IPv4 Using IS-IS (Cisco IOS XR) router isis DEFAULT net address-family ipv4 unicast metric-style wide segment-routing mpls segment-routing prefix-sid-map receive segment-routing prefix-sid-map advertise-local... segment-routing address-family ipv4 prefix-sid-map / range 8 Construct active mapping policy using remotely learned and locally configured mappings (mapping client) Advertise local mapping policy (mapping server) Local prefix-to-sid mapping policy / : /

69 Configuring a Mapping Client for SR and LDP Interworking for IPv4 Using IS-IS (Cisco IOS XR) router isis DEFAULT net address-family ipv4 unicast metric-style wide segment-routing mpls segment-routing prefix-sid-map receive interface Loopback0 passive address-family ipv4 unicast prefix-sid absolute interface GigabitEthernet0/0/0/0 point-to-point address-family ipv4 unicast Construct active mapping policy using remotely learned and locally configured mappings (mapping client) 69

70 Enabling Segment Routing Feature NXOS Commands: feature bgp install feature-set mpls feature-set mpls feature mpls l3vpn feature mpls segment-routing Under Interface configuration: mpls ip forwarding 70

71 Thank you

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