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PLNOG 17 - Leonir Hoxha - Next Generation Network Architecture - Segment Routing


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This session provides an overview of the Next Generation Network Architecture with Segment Routing technology that helps Service Providers to simplify the network. 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 beneficial to understand Segment Routing.

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PLNOG 17 - Leonir Hoxha - Next Generation Network Architecture - Segment Routing

  1. 1. Segment Routing Leonir Hoxha Network Consulting Engineer Cisco @ccie49534
  2. 2. Agenda • Drivers • Segment Routing model • Use cases • Summary
  3. 3. Why Segment Routing? Helping operators by tackling issues such as - Fast Reroute for any type of topology - Introduction of TI LFA - Operation simplicity, and scalable explicit routing (no midpoint state, RSVP-TE) - Smooth incremental deployment SDN ready - Offers a better and scalable interaction with orchestration, applications and the network. - Centralized or Distributed control plane
  4. 4. 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
  5. 5. Segment Routing – Forwarding Plane • MPLS: an ordered list of segments is represented as a stack of labels • Segment Routing re-uses MPLS data plane without any change • Segment represented as MPLS label • IPv6: an ordered list of segments is encoded in a routing extension header • SR Operations: PUSH, CONTINUE, NEXT. • This presentation: MPLS data plane
  6. 6. Global and Local Segments • Global Segment • Any node in SR domain understands associated instruction • Each node in SR domain installs the associated instruction in its forwarding table • MPLS: global label value in Segment Routing Global Block (SRGB) • Local Segment • Only originating node understands associated instruction • MPLS: locally allocated label
  7. 7. Global Segments – Global Label Indexes • Global Segments always distributed as a label range (SRGB) + Index • Index must be unique in Segment Routing Domain • Best practice: same SRGB on all nodes • “Global model”, requested by all operators • Global Segments are global label values, simplifying network operations • Default SRGB: 16,000 – 23,999 • All vendors also use this label range
  8. 8. IGP Segment Identifiers • Two basic building blocks distributed by IGP - Prefix Segments (also known as Node Segment) - Adjacency Segment (Adj-SID)
  9. 9. Node Segment ID • Shortest-path to the IGP prefix • Global Segment • Label = 16000 + Index • Advertised as index
  10. 10. Node Segment ID • Shortest-path to the IGP prefix - Equal Cost MultiPath (ECMP)-aware • Distributed by ISIS/OSPF - A node segment to 16078 distributes traffic across all ECMP paths to node O.
  11. 11. Adjacency Segment • C advertises the Adjacency Segment via ISIS • C is the only node to install the adjacency segment in FIB • Advertised as label value
  12. 12. Combining IGP Segments • Steer traffic on any path through the network • Path is specified by list of segments in packet header, a stack of labels • No path is signaled • No per-flow state is created • Single protocol: IS-IS or OSPF 1 2 3 4 5 16004 24045 16004 24045 Packet to 5 24045 Packet to 5 All nodes use default SRGB 16,000 – 23,999
  13. 13. Use Cases
  14. 14. Topology Independent LFA (TI-LFA) – Benefits • 100%-coverage across any topology • 50-msec Protection upon link, node or SRLG failure • Prevents transient congestion and suboptimal routing • leverages the post-convergence path, planned to carry the traffic • Avoid any intermediate flap via alternate path • Simple to operate and understand • automatically computed by the IGP • Incremental deployment • also protects LDP and IP traffic
  15. 15. Disjoint Routing • A to Z any plane • IGP shortest-path • PrefixSID of Z (16065) • A to Z via blue plane • SRTE policy pushes one additional Anycast segment “Blue” (16111) • Benefits • ECMP • No midpoint state
  16. 16. Centralized Traffic Engineering • Highly programmable and responsive to rapid changes. • Path Computation Element Protocol (PCEP) based controller • BGP-LS used for feeding information to the controller
  17. 17. • Future ready architecture considering Automation & Orchestration • Node/Link failure coverage, 100% with TI-LFA. • MicroLoop (uLoop) avoidance • Low Opex/Capex Summary SR hands-on demo?... contact me 
  18. 18. Questions?
  19. 19. Thanks… @ccie49534