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MPLS and Traffic Engineering

MPLS and Traffic Engineering. Zartash Afzal Uzmi Department of Computer Science Lahore University of Management Sciences (LUMS). Outline. Traditional IP Routing IP Routing Operation and Problems Motivation behind MPLS MPLS Terminology and Operation MPLS Label, LSR and LSP, LFIB Vs FIB

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MPLS and Traffic Engineering

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  1. MPLS and Traffic Engineering Zartash Afzal Uzmi Department of Computer Science Lahore University of Management Sciences (LUMS) MPLS and Traffic Engineering December 08, 2003

  2. Outline • Traditional IP Routing • IP Routing Operation and Problems • Motivation behind MPLS • MPLS Terminology and Operation • MPLS Label, LSR and LSP, LFIB Vs FIB • Transport of an IP packet over MPLS • Traffic Engineering [with MPLS] • Nomenclature • Requirements • Examples MPLS and Traffic Engineering December 08, 2003

  3. Traditional IP Routing • IP forwarding is done independently at every hop • IP forwarding decisions are made using: • Destination IP address (in packet header!) • Routing table (updated by routing algorithms!) • Each IP router runs its own instance of the routing algorithm • Each IP router makes its own forwarding decisions MPLS and Traffic Engineering December 08, 2003

  4. How IP Routing Works? Searching Longest Prefix Match in FIB (Too Slow) MPLS and Traffic Engineering December 08, 2003

  5. Problems with IP Routing • IP lookup (longest prefix matching) was a major bottleneck in high performance routers • This was made worse by the fact that IP forwarding requires complex lookup operation at every hop along the path MPLS and Traffic Engineering December 08, 2003

  6. Motivation behind MPLS • Avoid [slow] IP lookup • Provide traffic differentiation (QoS) Voice is really different from data! • Evolve routing functionality Control was too closely tied to forwarding! • Simplify deployment of IPv6 MPLS and Traffic Engineering December 08, 2003

  7. MPLS Label • To avoid IP lookup MPLS packets carry extra information called “Label” • Packet forwarding decision is made using label-based lookups • Labels have local significance only! Label IP Datagram MPLS and Traffic Engineering December 08, 2003

  8. LSR and LSP • Router that supports MPLS is known as label switching router (LSR) • Path which is followed by using labels is called label switched path (LSP) MPLS and Traffic Engineering December 08, 2003

  9. LFIB Vs FIB • Labels are searched in LFIB whereas normal IP Routing uses FIB to search longest prefix match for a destination IP address • Why switching based on labels is faster? • LFIB has fewer entries • Routing table FIB has very large number of entries • In LFIB Label is an exact match • In FIB IP is longest prefix match MPLS and Traffic Engineering December 08, 2003

  10. Transport of IP over MPLS Label Pushing: MPLS and Traffic Engineering December 08, 2003

  11. Transport of IP over MPLS Label Swapping: MPLS and Traffic Engineering December 08, 2003

  12. Transport of IP over MPLS Label Swapping: MPLS and Traffic Engineering December 08, 2003

  13. Transport of IP over MPLS Label Popping: MPLS and Traffic Engineering December 08, 2003

  14. Transport of IP over MPLS MPLS and Traffic Engineering December 08, 2003

  15. What is Traffic Engineering? • Performance optimization of operational networks • optimizing resource utilization • optimizing traffic performance • reliable network operation • How is traffic engineered? • measurement, modeling, characterization, and control of Internet traffic • Why? • high cost of network assets • service differentiation MPLS and Traffic Engineering December 08, 2003

  16. Hyperaggregation Problem • Routing Protocols Create A single "Shortest Path" MPLS and Traffic Engineering December 08, 2003

  17. Hyperaggregation Problem MPLS and Traffic Engineering December 08, 2003

  18. Nomenclature • Network Engineering • Put the bandwidth where the traffic is! • Physical cable deployment • Virtual connection provisioning • Traffic Engineering • Put the traffic where the bandwidth is! • Optimization of routes • Ability to “explicitly route” traffic MPLS and Traffic Engineering December 08, 2003

  19. 1 1 A B 1 2 C Traditional Traffic Engineering Traffic sent to A or B follows path with lowest metrics! MPLS and Traffic Engineering December 08, 2003

  20. 1 4 A B 1 2 C Traditional Traffic Engineering • Demerits of IGP-based traffic engineering • Changing traffic metric causes ALL the traffic to shift to the new path • Can not shift traffic destined only for A or only for B to the new path (through C) • Result is under or over utilization of some links MPLS and Traffic Engineering December 08, 2003

  21. Traffic Engineering: IGP vs. MPLS • Traditional TE (IGP based) • The ability to move traffic away from the shortest path calculated by the IGP to a less congested path • MPLS TE • Allows explicit routing and setup of LSPs • Provides recovery mechanisms failure • Enables Value added services • VPNs, SLAs, VoIP, etc. MPLS and Traffic Engineering December 08, 2003

  22. MPLS TE: How we may do it? MPLS and Traffic Engineering December 08, 2003

  23. MPLS TE: How we may do it? • LSPs are set up by LSRs based on information they learn from routing protocols (IGPs) • This defeats the purpose! • If we were to use “shortest path”, IGP was okay MPLS and Traffic Engineering December 08, 2003

  24. MPLS TE: How we actually do it? • MPLS TE Requires: • Enhancements to routing protocols • OSPF-TE and ISIS-TE • Enhancement to signaling protocols to allow explicit constraint based routing • RSVP-TE and CR-LDP • Constraint based routing • Explicit route selection • Recovery mechanisms defined MPLS and Traffic Engineering December 08, 2003

  25. Signaling Mechanisms • RSVP-TE • Extensions to RSVP for traffic engineering • BGP-4 • Carrying label information in BGP-4 • CR-LDP • A label distribution protocol that distributes labels determined based on constraint based routing MPLS and Traffic Engineering December 08, 2003

  26. RSVP-TE • Basic flow of LSP set-up using RSVP MPLS and Traffic Engineering December 08, 2003

  27. RSVP-TE PATH Message • PATH message is used to establish state and request label assignment • R1 transmits a PATH message addressed to R9 MPLS and Traffic Engineering December 08, 2003

  28. RSVP-TE RESV Message • RESV is used to distribute labels after reserving resources • R9 transmits a RESV message, with label=3, to R8 • R8 and R4 store “outbound” label and allocate an “inbound” label. They also transmits RESV with inbound label to upstream LSR • R1 binds label to forwarding equivalence class (FEC) MPLS and Traffic Engineering December 08, 2003

  29. Rerouting LSP Tunnels • When a more “optimal” route/path becomes available • When a failure of a resource occurs along a TE LSP • Make-before-break mechanism • Adaptive, smooth rerouting and traffic transfer before tearing down the old LSP • Not disruptive to traffic MPLS and Traffic Engineering December 08, 2003

  30. Recovering LSP Tunnels LSP Set-up MPLS and Traffic Engineering December 08, 2003

  31. Protection LSP set up MPLS and Traffic Engineering December 08, 2003

  32. Protection LSP MPLS and Traffic Engineering December 08, 2003

  33. References • RFC 2702 “Requirements for Traffic Engineering Over MPLS” • RFC 3031 “Multiprotocol Label Switching Architecture” • RFC 3272 “Overview and Principles of Internet Traffic Engineering” • RFC 3346 “Applicability Statement for Traffic Engineering with MPLS” • MPLS Forum (http://www.mplsforum.org) MPLS and Traffic Engineering December 08, 2003

  34. Data Upstream and downstream LSR Upstream Downstream 172.68.10/24 LSR1 LSR2 MPLS and Traffic Engineering December 08, 2003

  35. Egress LSR Ingress LSR How MPLS Works Searching Longest Prefix Match in FIB (Too Slow) MPLS and Traffic Engineering December 08, 2003

  36. Use label 5 for destination 171.68.32/24 MPLS Data Packet with label 5 travel Label Distribution ALWAYS, Downstream to upstream label distribution 171.68.32/24 LSR2 LSR1 MPLS and Traffic Engineering December 08, 2003

  37. Send label Without any Request Downstream Un-solicited Upstream Upstream 171.68.32/24 LSR2 LSR1 MPLS and Traffic Engineering December 08, 2003

  38. Send label ONLY after receiving request Request For label Downstream On Demand (DoD) Down Stream Upstream 171.68.32/24 LSR2 LSR1 MPLS and Traffic Engineering December 08, 2003

  39. Egress LSR Ingress LSR Ordered Label Distribution Label MPLS and Traffic Engineering December 08, 2003

  40. Egress LSR Ingress LSR Unordered Label Distribution Label Label MPLS and Traffic Engineering December 08, 2003

  41. Label Retention Modes 1. Liberal Retention Mode 2. Conservative Retention Mode ? Destination Label LSR1 Label MPLS and Traffic Engineering December 08, 2003

  42. Label Distribution Modes Label distribution modes Advertisement Distribution Downstream-on-Demand Downstream-Unsolicited Independent Ordered Retention Liberal Conservative MPLS and Traffic Engineering December 08, 2003

  43. Ingress LSR for LSP1 LSP1 Egress LSR for LSP1 LSP3 LSP2 Hierarchical LSP Ingress LSR for LSP3 MPLS and Traffic Engineering December 08, 2003

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