1. Introduction to MPLS and Traffic Engineering Zartash Afzal Uzmi

2. Jan 11, 2006Lahore University of Management Sciences2 First slide… Questions? Ask when you have them!

3. Jan 11, 2006Lahore University of Management Sciences3 Outline Traditional IP Routing Forwarding and routing Problems with IP routing Motivations behind MPLS MPLS Terminology and Operation MPLS Label, LSR and LSP, LFIB Vs FIB Transport of an IP packet over MPLS More MPLS terminology Traffic Engineering [with MPLS] Nomenclature Requirements Examples

4. Jan 11, 2006Lahore University of Management Sciences4 Outline Traditional IP Routing Forwarding and routing Problems with IP routing Motivations behind MPLS MPLS Terminology and Operation MPLS Label, LSR and LSP, LFIB Vs FIB Transport of an IP packet over MPLS More MPLS terminology Traffic Engineering [with MPLS] Nomenclature Requirements Examples

5. Jan 11, 2006Lahore University of Management Sciences5 Forwarding and routing Forwarding: Passing a packet to the next hop router Routing: Computing the “best” path to the destination IP routing – includes routing and forwarding Each router makes the forwarding decision Each router makes the routing decision MPLS routing Only one router (source) makes the routing decision Intermediate router make the forwarding decision

6. Jan 11, 2006Lahore University of Management Sciences6 IP versus MPLS routing IP routing Each IP datagram is routed independently Routing and forwarding is destination-based Routers look at the destination addresses May lead to congestion in parts of the network MPLS routing A path is computed “in advance” and a “virtual circuit” is established from ingress to egress An MPLS path from ingress to egress node is called a label switched path (LSP)

7. Jan 11, 2006Lahore University of Management Sciences7 How IP routing works Searching Longest Prefix Match in FIB (Too Slow)

8. Jan 11, 2006Lahore University of Management Sciences8 Problems with IP routing Too slow 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 Too rigid – no flexibility Routing decisions are destination-based Not scalable in some desirable applications When mapping IP traffic onto ATM

9. Jan 11, 2006Lahore University of Management Sciences9 IP routing rigidity example Packet 1: Destination A Packet 2: Destination B S computes shortest paths to A and B; finds D as next hop Both packets will follow the same path Leads to IP hotspots! Solution? Try to divert the traffic onto alternate paths 11 12 A B C A B S D

10. Jan 11, 2006Lahore University of Management Sciences10 IP routing rigidity example Increase the cost of link DA from 1 to 4 Traffic is diverted away from node D A new IP hotspot is created! Solution(?): Network Engineering Put more bandwidth where the traffic is! Leads to underutilized links; not suitable for large networks 14 12 A B C S A B D

11. Jan 11, 2006Lahore University of Management Sciences11 Motivations behind MPLS Avoid [slow] IP lookup Led to the development of IP switching in 1996 Provide some scalability for IP over ATM Evolve routing functionality Control was too closely tied to forwarding Evolution of routing functionality led to some other benefits Explicit path routing Provision of service differentiation (QoS)

12. Jan 11, 2006Lahore University of Management Sciences12 IP routing versus MPLS routing Traditional IP Routing Multiprotocol Label Switching (MPLS) SD 54 3 21 MPLS allows overriding shortest paths!

13. Jan 11, 2006Lahore University of Management Sciences13 Outline Traditional IP Routing Forwarding and routing Problems with IP routing Motivations behind MPLS MPLS Terminology and Operation MPLS Label, LSR and LSP, LFIB Vs FIB Transport of an IP packet over MPLS More MPLS terminology Traffic Engineering [with MPLS] Nomenclature Requirements Examples

14. Jan 11, 2006Lahore University of Management Sciences14 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! How routing along explicit path works? IP DatagramLabel

15. Jan 11, 2006Lahore University of Management Sciences15 Routing along explicit paths Idea: Let the source make the complete routing decision How is this accomplished? Let the ingress attach a label to the IP packet and let intermediate routers make forwarding decisions only On what basis should you choose different paths for different flows? Define some constraints and hope that the constraints will take “some” traffic away from the hotspot! Use CSPF instead of SPF (shortest path first)

16. Jan 11, 2006Lahore University of Management Sciences16 Label, LSP and LSR Label Router that supports MPLS is known as label switching router (LSR) An “Edge” LSR is also known as LER (edge router) Path which is followed using labels is called LSP Label = 20 bits Exp = Experimental, 3 bits S = Bottom of stack, 1bit TTL = Time to live, 8 bits 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 Label | Exp|S| TTL

17. Jan 11, 2006Lahore University of Management Sciences17 LFIB versus 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

18. Jan 11, 2006Lahore University of Management Sciences18 Mpls Flow Progress LSR1 LSR2 LSR3 LSR5 LSR6 R1R2LSR4 D 1 - R1 receives a packet for destination D connected to R2 R1 and R2 are regular routers D destination

19. Jan 11, 2006Lahore University of Management Sciences19 Mpls Flow Progress LSR1 LSR2 LSR3 LSR5 LSR6 R1R2LSR4 D 2 - R1 determines the next hop as LSR1 and forwards the packet (Makes a routing as well as a forwarding decision) D destination

20. Jan 11, 2006Lahore University of Management Sciences20 Mpls Flow Progress LSR1 LSR2 LSR3 LSR5 LSR6 R1R2LSR4 D 3 – LSR1 establishes a path to LSR6 and “PUSHES” a label (Makes a routing as well as a forwarding decision) D destination 31

21. Jan 11, 2006Lahore University of Management Sciences21 Mpls Flow Progress LSR1 LSR2 LSR3 LSR5 LSR6 R1R2LSR4 D 4 – LSR3 just looks at the incoming label LSR3 “SWAPS” with another label before forwarding D destination 17 Labels have local signifacance!

22. Jan 11, 2006Lahore University of Management Sciences22 MPLS Flow Progress LSR1 LSR2 LSR3 LSR5 LSR6 R1R2LSR4 D 5 – LSR6 looks at the incoming label LSR6 “POPS” the label before forwarding to R2 D destination 17 Path within MPLS cloud is pre-established: LSP (label-switched path)

23. Jan 11, 2006Lahore University of Management Sciences23 MPLS and explicit routing recap Who establishes the LSPs in advance? Ingress routers How do ingress routers decide not to always take the shortest path? Ingress routers use CSPF (constrained shortest path first) instead of SPF Examples of constraints: Do not use links left with less than 7Mb/s bandwidth Do not use blue-colored links for this request Use a path with delay less than 130ms

24. Jan 11, 2006Lahore University of Management Sciences24 CSPF What is the mechanism? First prune all links not fulfilling constrains Now find shortest path on the rest of the topology Requires some reservation mechanism Changing state of the network must also be recorded and propagated For example, ingress needs to know how much bandwidth is left on links The information is propagated by means of routing protocols and their extensions

25. Jan 11, 2006Lahore University of Management Sciences25 More MPLS terminology 172.68.10/24 LSR1LSR2 UpstreamDownstream Data

26. Jan 11, 2006Lahore University of Management Sciences26 Label advertisement Always downstream to upstream label advertisement and distribution 171.68.32/24 LSR1 LSR2 Use label 5 for destination 171.68.32/24 MPLS Data Packet with label 5 travels Upstream Downstream

27. Jan 11, 2006Lahore University of Management Sciences27 Label advertisement Label advertisement can be downstream unsolicited or downstream on-demand 171.68.32/24 LSR1 LSR2 Sends label Without any Request Upstream Downstream 171.68.32/24 LSR1LSR2 Sends label ONLY after receiving request Request For label Upstream Downstream

28. Jan 11, 2006Lahore University of Management Sciences28 Label distribution Label distribution can be ordered or unordered First we see an example of ordered label distribution Ingress LSR Egress LSR Label

29. Jan 11, 2006Lahore University of Management Sciences29 Label distribution Label distribution can be ordered or unordered Next we see an example of unordered label distribution Ingress LSR Egress LSR Label

30. Jan 11, 2006Lahore University of Management Sciences30 Label retention modes Label retention can be conservative or liberal LSR1 Destination Label ?

31. Jan 11, 2006Lahore University of Management Sciences31 Label operations Advertisement Downstream unsolicited Downstream on-demand Distribution Ordered Unordered Retention Liberal Conservative

32. Jan 11, 2006Lahore University of Management Sciences32 Outline Traditional IP Routing Forwarding and routing Problems with IP routing Motivations behind MPLS MPLS Terminology and Operation MPLS Label, LSR and LSP, LFIB Vs FIB Transport of an IP packet over MPLS More MPLS terminology Traffic Engineering [with MPLS] Nomenclature Requirements Examples

33. Traffic Engineering Traffic Engineering with MPLS (Application of CSPF)

34. Jan 11, 2006Lahore University of Management Sciences34 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

35. Jan 11, 2006Lahore University of Management Sciences35 Traffic engineering Recall the IP hotspot problem The ability to move traffic away from the shortest path calculated by the IGP (such as OSPF) to a less congested path IP: changing a metric will cause ALL the traffic to divert to the less congested path MPLS: allows explicit routing (using CSPF) and setup of such explicitly computed LSPs

36. Jan 11, 2006Lahore University of Management Sciences36 MPLS-TE: How to 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

37. Jan 11, 2006Lahore University of Management Sciences37 MPLS TE: How we actually do it? MPLS TE Requires: Enhancements to routing protocols OSPF-TE 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

38. Jan 11, 2006Lahore University of Management Sciences38 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 RSVP-TE and CR-LDP both do label distribution and path reservation – use any one of them!

39. Jan 11, 2006Lahore University of Management Sciences39 RSVP-TE Basic flow of LSP set-up using RSVP

40. Jan 11, 2006Lahore University of Management Sciences40 RSVP-TE PATH Message PATH message is used to establish state and request label assignment R1 transmits a PATH message addressed to R9

41. Jan 11, 2006Lahore University of Management Sciences41 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)

42. Jan 11, 2006Lahore University of Management Sciences42 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

43. Jan 11, 2006Lahore University of Management Sciences43 Recovering LSP tunnels LSP Set-up

44. Jan 11, 2006Lahore University of Management Sciences44 Protection LSP set up

45. Jan 11, 2006Lahore University of Management Sciences45 Protection LSP

46. Jan 11, 2006Lahore University of Management Sciences46 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)

47. Jan 11, 2006Lahore University of Management Sciences47 Last slide… Thank you! Questions?

48. Jan 11, 2006Lahore University of Management Sciences48 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to restoration routing Local Restoration: Types of Backup Paths Local Restoration: Fault Models Backup Bandwidth Sharing Activation sets Restoration routing framework Components Typical example Evaluation and Experimentation

49. Jan 11, 2006Lahore University of Management Sciences49 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to restoration routing Local Restoration: Types of Backup Paths Local Restoration: Fault Models Backup Bandwidth Sharing Activation sets Restoration routing framework Components Typical example Evaluation and Experimentation

50. Jan 11, 2006Lahore University of Management Sciences50 Network Traffic and Services Network Traffic today Not what it was 10 years ago Multimedia intensive New and interactive applications are emerging Internet telephony Videoconferencing Streaming media (voice and video) Remote collaboration (e.g., remote desktop) Many new applications are real-time More and more users of these applications Burstiness behavior has changed over the years!

51. Jan 11, 2006Lahore University of Management Sciences51 Current Network Architecture Internet is popular because It is inexpensive Internet is inexpensive because It uses resource sharing by means of statistical multiplexing Current Internet architecture Uses packet switches with buffers Required buffer size is primarily determined by a random traffic pattern Buffer size optimization Too low  High drop rate Too high  High delay

52. Jan 11, 2006Lahore University of Management Sciences52 Architectural Requirements Emerging applications Two-way interactive communications One-way streaming media type applications Under normal conditions We are worried about the two-way interactive applications When resources fail We are also worried about the one-way applications Current Internet architecture is not suitable for new and emerging applications New architectures are being researched

53. Jan 11, 2006Lahore University of Management Sciences53 Architectural Requirements New network architectures All circuit-switched? Mix of packet-switch and “circuit-switch-like” Experience with networks Bigger buffers are required when there is more randomness and more aggregation Should use circuits at places where we see more randomness Example: 100x100 project Edge network is packet-switched Core network is virtual-circuits

54. Jan 11, 2006Lahore University of Management Sciences54 IP versus MPLS In IP Routing, each router makes its own routing and forwarding decisions In MPLS: source router makes the routing decision Intermediate routers make forwarding decisions A path is computed and a “virtual circuit” is established from ingress router to egress router An MPLS path or virtual circuit from source to destination is called an LSP (label switched path)

55. Jan 11, 2006Lahore University of Management Sciences55 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to restoration routing Local Restoration: Types of Backup Paths Local Restoration: Fault Models Backup Bandwidth Sharing Activation sets Restoration routing framework Components Typical example Evaluation and Experimentation

56. Jan 11, 2006Lahore University of Management Sciences56 Restoration in IP network In traditional IP, what happens when a link or node fails? Information needs to be disseminated in the network During this time, packets may go in loops Restoration latency is in the order of seconds We look for restoration possibilities in an MPLS network

57. Jan 11, 2006Lahore University of Management Sciences57 QoS Requirements Bandwidth Guaranteed Primary Paths Bandwidth Guaranteed Backup Paths BW remains provisioned in case of network failure Minimal “Restoration Latency” Restoration latency is the time that elapses between the occurrence of a failure and the diversion of network traffic on a new path Path Restoration  More Latency Local Restoration  Less Latency

58. Jan 11, 2006Lahore University of Management Sciences58 Restoration in MPLS S123D Primary Path Backup Path Path Protection This type of “path Protection” still takes 100s of ms. We may explore “Local Protection” to quickly switch onto backup paths!

59. Jan 11, 2006Lahore University of Management Sciences59 Local Restoration: Fault Models ABCD Link Protection ABCD ABCD Node Protection Element Protection

60. Jan 11, 2006Lahore University of Management Sciences60 nhop and nnhop paths Primary Path Backup Path All links and all nodes are protected! AB C D E PLR: Point of Local Repair nnhop nhop

61. Jan 11, 2006Lahore University of Management Sciences61 Opportunity cost of backup paths Local Protection requires that backup paths are setup in advance Upon failure, traffic is promptly switched onto preset backup paths Bandwidth must be reserved for all backup paths This results in a reduction in the number of Primary LSPs that can otherwise be placed on the network Can we reduce the amount of “backup bandwidth” but still provide guaranteed backups?

62. Jan 11, 2006Lahore University of Management Sciences62 BW Sharing in backup Paths Example: max(X, Y) BW: Y AB CD E F G L1 L2 BW: X Primary Path Backup Path X X X YY X+YX+YSharing

63. Jan 11, 2006Lahore University of Management Sciences63 Activation Sets A B C D E Activation set for node BActivation set for link (A,B) A B C D E

64. Jan 11, 2006Lahore University of Management Sciences64 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to restoration routing Local Restoration: Types of Backup Paths Local Restoration: Fault Models Backup Bandwidth Sharing Activation sets Restoration routing framework Components Typical example Evaluation and Experimentation

65. Jan 11, 2006Lahore University of Management Sciences65 Restoration Routing Frameworks We look to answer the following questions? Who computes the primary path? What is the fault model (link, node, or element protection)? Where do the backup paths originate? Who computes the backup path? At what point do the backup paths merge back with the primary path What information is stored locally in the nodes/routers What information is propagated through routing protocols What if a primary path can not be fully protected The goal is almost always to maximize bandwidth sharing Performance criteria is almost always the maximum number of LSPs that can be placed on the network

66. Jan 11, 2006Lahore University of Management Sciences66 Evaluation & Experimentation Traffic Generation Use existing or emerging traffic models Consider call holding times and multi-service traffic Rejected Requests Experiments Measure the number of rejected requests Simulate on various topologies Network Loading Experiments Set link capacities to infinity Measure the total bandwidth required to service a given set of requests Simulate on various topologies

67. Jan 11, 2006Lahore University of Management Sciences67 Recent Trends Preemption of lower class traffic Multilayer recovery We can “almost” deal with recovery at a single protocol layer What if we intend to provide recovery at multiple protocol layers? For multilayer recovery, we need to consider these additional issues: Interworking of layers Local information stored at each node of each layer Recovery provided by each individual layer Signaling mechanism from one layer to another Effects on bandwidth sharing (if sharing is used)

68. Jan 11, 2006Lahore University of Management Sciences68 Thank You! Questions & Answers

69. Jan 11, 2006Lahore University of Management Sciences69 Extra Stuff!

70. Jan 11, 2006Lahore University of Management Sciences70 Extent of BW Sharing: oAIS Aggregate Information Scenario (AIS) F ij : Bandwidth reserved on link (i, j) for all primary LSPs G ij : Bandwidth reserved on link (i, j) for all backup LSPs Optimized AIS (oAIS) – (H ij instead of F ij ) Hij : Maximum bandwidth reserved on any one link by all backup paths spanning link (i, j) More Information propagated  More potential for BW sharing

71. Jan 11, 2006Lahore University of Management Sciences71 oAIS versus AIS: Example LSP Request-1 (src, dst, bw) = (A, C, 4) A F D E BC G F AB =4 H AB =4 G AF =4

72. Jan 11, 2006Lahore University of Management Sciences72 oAIS Example LSP Request-2 (src, dst, bw) = (A, C, 5) A F D E BC G F AB =9 H AB =5 G AF =4 G AG =5 F AB =4 H AB =4

73. Jan 11, 2006Lahore University of Management Sciences73 oAIS Example LSP Request-3 (src, dst, bw) = (D, E, 7) A F D E BC G F AB =9 H AB =5 G AF =4 G AG =5 F DE =7 G AF =7

74. Jan 11, 2006Lahore University of Management Sciences74 oAIS Example LSP Request-4 (src, dst, bw) = (A, C, 6) A F D E BC G F AB =9 G AF =7 G AG =5 F DE =7 Need to Evaluate cost of all possible backup paths? How much BW is shareable on (A, F)? AIS: Shareable = max(0, G AF - F AB ) = G AF - min(G AF, F AB ) = 0 Additional resv = 6 oAIS: (H AB ≤ F AB ) Shareable = G AF - min(G AF, H AB ) = 2 Additional resv = 6 - 2 = 4 CIS: (link (A,B) knows BW red ) Shareable = G AF - BW red = 7 - 4 = 3 Additional resv = 6 - 3 = 3 H AB =5

75. Jan 11, 2006Lahore University of Management Sciences75 Single Link Protection: Network 1

76. Jan 11, 2006Lahore University of Management Sciences76 Single Link Protection: Network 1

77. Jan 11, 2006Lahore University of Management Sciences77 Single Link Protection: Network 2

78. Jan 11, 2006Lahore University of Management Sciences78 Single Link Protection: Network 2

79. Jan 11, 2006Lahore University of Management Sciences79 Single Node Protection: Network 1

80. Jan 11, 2006Lahore University of Management Sciences80 Single Element Protection: Network 1

81. Jan 11, 2006Lahore University of Management Sciences81 A Bandwidth Sharing Model Primary Path Backup Path All links and all nodes are protected! (Simplified for the Link Protection Fault Model) Recall the definition of nhop paths ABCD Link Protection

82. Jan 11, 2006Lahore University of Management Sciences82 Bandwidth Sharing Model Previous: A ij := Set of all primaries traversing through (i, j) B uv := Set of all backups traversing through (u, v) New definition (specialized for link protection case): A ij := Set of all primaries traversing through (i, j) B uv := Set of all nhop paths traversing through (u, v) µ ij := Set of all nhop paths that span (i, j)  ij uv := B uv ∩ µ ij (set of paths falling on (u,v) if (i,j) fails)

83. Jan 11, 2006Lahore University of Management Sciences83 Bandwidth Sharing Model i uv j k RED=7 BLU=2 3 OLD MODEL: A ij = {R, B} B uv = {R, B, …} A ij ∩ B uv = {R, B} || A ij ∩ B uv || = 2+7 = 9 Un-shareable = 9 Shareable = 10 - 9 = 1 GRN=3 (New Request) Guv = 10 NEW MODEL: A ij = {R, B} B uv = {nh ij r, nh ij b, …}(nhops through (u, v)) µ ij = {nh ij r, nh ij b, …}(nhops spanning (i, j))  ij uv = µ ij ∩ B uv = {nh ij r, nh ij b } ||  ij uv || = 2 + 7 = 9(Un-shareable) Shareable = G uv - ||  ij uv || = 10 - 9 = 1

84. Jan 11, 2006Lahore University of Management Sciences84 Bandwidth Sharing Model i uv j k RED=7 BLU=2 3 OLD MODEL: A ij = {R, B} B uv = {R, B, …} A ij ∩ B uv = {R, B} || A ij ∩ B uv || = 2+7 = 9 Un-shareable = 9 Shareable = 10 - 9 = 1 NEW MODEL: A ij = {R, B} B uv = {nh ij r, nh jk b, …}(nhops through (u, v)) µ ij = {nh ij r, nh ij b, …}(nhops spanning (i, j))  ij uv = µ ij ∩ B uv = {nh ij r } ||  ij uv || = 7(Un-shareable) Shareable = G uv - ||  ij uv || = 10 - 7 = 3 GRN=3 (New Request) Guv = 10

85. Jan 11, 2006Lahore University of Management Sciences85 Restoration in MPLS Primary Path Backup Path Path Protection MPLS path Protection may take 100s of ms, whereas MPLS Local protection takes less than 10 ms. AB CDE