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Multi-Protocol Label Switching MPLS

Multi-Protocol Label Switching MPLS. Outline. Virtualisation Overview Label Encapsulations Label Distribution Protocols Constraint Based Routing with CR-LDP Summary. Virtualization of networks. Virtualization of resources: a powerful abstraction in systems engineering:

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Multi-Protocol Label Switching MPLS

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  1. Multi-Protocol Label SwitchingMPLS

  2. Outline • Virtualisation • Overview • Label Encapsulations • Label Distribution Protocols • Constraint Based Routing with CR-LDP • Summary

  3. Virtualization of networks Virtualization of resources: a powerful abstraction in systems engineering: • computing examples: virtual memory, virtual devices • Virtual machines: e.g., java • IBM VM os from 1960’s/70’s • layering of abstractions: don’t sweat the details of the lower layer, only deal with lower layers abstractly

  4. The Internet: virtualizing networks … differing in: • addressing conventions • packet formats • error recovery • routing 1974: multiple unconnected nets • ARPAnet • data-over-cable networks • packet satellite network (Aloha) • packet radio network satellite net ARPAnet "A Protocol for Packet Network Intercommunication", V. Cerf, R. Kahn, IEEE Transactions on Communications, May, 1974, pp. 637-648.

  5. Internetwork layer (IP): • addressing: internetwork appears as a single, uniform entity, despite underlying local network heterogeneity • network of networks The Internet: virtualizing networks Gateway: • “embed internetwork packets in local packet format or extract them” • route (at internetwork level) to next gateway gateway satellite net ARPAnet

  6. Cerf & Kahn’s Internetwork Architecture What is virtualized? • two layers of addressing: internetwork and local network • new layer (IP) makes everything homogeneous at internetwork layer • underlying local network technology • cable • satellite • 56K telephone modem • today: ATM, MPLS … “invisible” at internetwork layer. Looks like a link layer technology to IP!

  7. ATM and MPLS • ATM, MPLS separate networks in their own right • different service models, addressing, routing from Internet • viewed by Internet as logical link connecting IP routers • just like dialup link is really part of separate network (telephone network)

  8. Asynchronous Transfer Mode: ATM • 1990’s/00 standard for high-speed (155Mbps to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture • Goal:integrated, end-end transport of carry voice, video, data • meeting timing/QoS requirements of voice, video (versus Internet best-effort model) • “next generation” telephony: technical roots in telephone world • packet-switching (fixed length packets, called “cells”) using virtual circuits

  9. ATM architecture • adaptation layer: only at edge of ATM network • data segmentation/reassembly • roughly analogous to Internet transport layer • ATM layer: “network” layer • cell switching, routing • physical layer

  10. ATM: network or link layer? Vision: end-to-end transport: “ATM from desktop to desktop” • ATM is a network technology Reality: used to connect IP backbone routers • “IP over ATM” • ATM as switched link layer, connecting IP routers IP network ATM network

  11. ATM Layer: Virtual Circuits • VC transport: cells carried on VC from source to dest • call setup, teardown for each call before data can flow • each packet carries VC identifier (not destination ID) • every switch on source-dest path maintain “state” for each passing connection • link,switch resources (bandwidth, buffers) may be allocated to VC: to get circuit-like perf. • Permanent VCs (PVCs) • long lasting connections • typically: “permanent” route between two IP routers • Switched VCs (SVC): • dynamically set up on per-call basis

  12. ATM VCs • Advantages of ATM VC approach: • QoS performance guarantee for connection mapped to VC (bandwidth, delay, delay jitter) • Drawbacks of ATM VC approach: • Inefficient support of datagram traffic • one PVC between each source/dest pair) does not scale (N*2 connections needed) • SVC introduces call setup latency, processing overhead for short lived connections

  13. What Is MPLS? • A switched fowarding technique based on IP • Delivers explicit, switched forwarding to IP-based internetworks • IETF Goals • Higher performance • Routing table efficiency • Frame/Cell integration • DiffServ • "New" Goals • Traffic engineering • DiffServ

  14. Goals of Multiprotocol Label Switching • MPLS extends traditional IP in the following areas: • Simplified Forwarding • Based on labels instead of longest prefix-match • Efficient Explicit Routing • Route is specified once by source at path setup time • Traffic Engineering • Split traffic load over multiple parallel or alternate routes • QoS Routing • Select routes based upon QoS requirements • Non-trivial Mappings of IP Datagrams onto Paths • Performed only at network edges/borders

  15. IP MPLS+IP ATM BEST OF BOTH WORLDS CIRCUITSWITCHING PACKETForwarding HYBRID • MPLS + IP form a middle ground that combines the best of IP and the best of circuit switching technologies. • ATM and Frame Relay cannot easily come to the middle so IP has!!

  16. MPLS Terminology • The Easy Stuff • Label • Label Switch Router • Label Switch Path • Label Information Base • Forwarding Equivalence Class • The Harder Stuff • Label Distribution Protocol • Constraint-Based LDP (CR-LDP) • RSVP for Traffic Engineering (RSVP-TE)

  17. Label Encapsulation ATM FR Ethernet PPP L2 VPI VCI DLCI “Shim Label” Label “Shim Label” ……. IP | PAYLOAD MPLS Encapsulation is specified over various media types. Top labels may use existing format, lower label(s) use a new “shim” label format.

  18. Label Structure MPLS "shim" headers ... Layer 2 Header IP Packet Label Exp. S TTL 4 Octets Label: 20-bit value, (0-16 reserved) Exp.: 3-bits Experimental (former ToS) S: 1-bit Bottom of stack TTL: 8-bits Time To Live

  19. LANE#1 TURN RIGHT USE LANE#2 Label Substitution Have a friend go to B ahead of you using one of the previous two techniques. At every road they reserve a lane just for you. At ever intersection they post a big sign that says for a given lane which way to turn and what new lane to take. LANE#1 LANE#2

  20. IP #L1 IP #L2 IP #L3 ROUTE AT EDGE, SWITCH IN CORE IP IP IP Forwarding IP Forwarding LABEL SWITCHING

  21. Embedded MPLS Labels Layer 2 Header Label 1 Label 2 Label 3 IP Packet MPLS Domain 1 MPLS Domain 2 MPLS Domain 3

  22. "Concentric" or "Sequential" Layer 2 Header Label 1 Label 2 Label 3 IP Packet MPLS Domain 1 MPLS Domain 2 MPLS Domain 3 SP 1 SP 2 SP 3

  23. Switch Applications Switch Control Processor INPUTS OUTPUTS 10 - 40G Fabric(s) BUFFER MANAGEMENT OUTPUT BUFFER Label Switch Router Architecture Smart Connections Pre-computation PNNI routing PNNI signaling OSPF(TE), IS-IS(TE), BGP4 RSVP-TE, CR-LDP Per Port Per Priority Per Flow Queuing Flow Merging Policing Marking IP Forwarding Labeling Classification Buffer Allocation Packet Drop Hierarchical Scheduler Shaper

  24. IP 47.1.1.1 1 47.1 2 1 47.3 47.2 IP 47.1.1.1 Label Edge Routers • Label Edge Router (LER) • A tunnel (LSP) endpoint • Ingress • Egress • Push and Pop LER 10 MB LER 40 MB

  25. IP 47.1.1.1 1 47.1 2 1 47.3 47.2 IP 47.1.1.1 Label Switch Router • Label Switch Router (LSR) • A tunnel transit point • active LSR LSR LSR LSR

  26. Label Switch Path • The path followed by packets that have the same label! IP Source Network IP Destination Network The Internet

  27. Label Information Base (LIB) • The LSR routing table where a label ID is associated with an outbound port IP Source Network IP Destination Network Label (In) Label (Out) O/P Port 12 766 Ser_1 The Internet 308 5 Ser_2

  28. IP1 IP1 IP1 IP2 IP1 IP2 IP1 IP2 #L1 #L1 #L2 #L3 #L3 #L2 IP2 IP2 Forwarding Equivalence Classes LSR LSR LER LER LSP Packets are destined for different address prefixes, but can be mapped to common path • FEC = “A subset of packets that are all treated the same way by a router” • The concept of FECs provides for a great deal of flexibility and scalability • In conventional routing, a packet is assigned to a FEC at each hop (i.e. L3 look-up), in MPLS it is only done once at the network ingress.

  29. MPLS Routing Protocols By jove! These look familiar! • OSPF • BGP • ISIS

  30. Routing Protocols • Required for topology determination • Existing Routing Protocols Can Be Used With MPLS… • But they do not support ER/TE • Modifications To OSPF, ISIS and BGP Are In Draft

  31. MPLS: Partitioning Routing and Forwarding Routing Based on: Classful Addr. Prefix? Classless Addr. Prefix? Multicast Addr.? Port No.? ToS Field? OSPF, IS-IS, BGP, RIP Forwarding Table Forwarding Based on: Exact Match on Fixed Length Label MPLS • Current network has multiple forwarding paradigms • - class-ful longest prefix match (Class A,B,C boundaries) • - classless longest prefix match (variable boundaries) • - multicast (exact match on source and destination) • - type-of-service (longest prefix. match on addr. + exact match on ToS) • As new routing methods change, new route look-up algorithms are required • - introduction of CIDR • Next generation routers will be based on hardware for route look-up • - changes will require new hardware with new algorithm • MPLS has a consistent algorithm for all types of forwarding; partitions routing/fwding • - minimizes impact of the introduction of new forwarding methods MPLS introduces flexibility through consistent forwarding paradigm

  32. Routing & Label Distribution • Label Assignment • Control-Driven • Topology-Driven • Request-Driven • Traffic Driven

  33. Label Distribution Options • Manual LIB Entries • Analogous To Static Routes • Will Not Scale • May Be Used In Early Interoperability Tests and Trade Show Demos • Label Distribution Protocols • "A set of procedures by which one Label Switched Router (LSR) informs another of the label/FEC bindings it has made"

  34. Scenario ... 1.3 C.3 IP Source Network Router1 Router2 IP Destination Network 1.1 C.1 B.2 2.1 LSR2 LSR3 5.1 5.2 3.2 A.1 3.1 LSR4 LSR1 A.2 2.2 LSR5 B.1 LSR6 MPLS Domain

  35. Now Let's Fill The LIBs Routing Table or LIB Inbound Label Outbound Label Dest. Net Next Hop I/F ID Router 1 None None C.0 2.2 Ser_1 LSR 1 None 12* C.0 N/A Ser_2 LSR 2 12 4 N/A N/A Ser_2 LSR 3 4 8 N/A N/A Ser_2 LSR 5 8 None** C.0 B.2 Ser_4 Router 2 C.0 C.0 C.0 Direct Eth_4 * Label appended ** Label stripped N/A = This field not parsed

  36. Now Let's Fill The LIBs Routing Table or LIB Inbound Label Outbound Label Dest. Net Next Hop I/F ID Router 1 None None C.0 2.2 Ser_1 LSR 1 None 12* C.0 N/A Ser_2 LSR 2 12 4 N/A N/A Ser_2 LSR 3 4 8 N/A N/A Ser_2 LSR 5 8 None** C.0 B.2 Ser_4 Router 2 C.0 C.0 C.0 Direct Eth_4 * Label appended ** Label stripped N/A = This field not parsed

  37. Now Let's Fill The LIBs Routing Table or LIB Inbound Label Outbound Label Dest. Net Next Hop I/F ID Router 1 None None C.0 2.2 Ser_1 LSR 1 None 12* C.0 N/A Ser_2 LSR 2 12 4 N/A N/A Ser_2 LSR 3 4 8 N/A N/A Ser_2 LSR 5 8 None** C.0 B.2 Ser_4 Router 2 C.0 C.0 C.0 Direct Eth_4 * Label appended ** Label stripped N/A = This field not parsed

  38. Now Let's Fill The LIBs Routing Table or LIB Inbound Label Outbound Label Dest. Net Next Hop I/F ID Router 1 None None C.0 2.2 Ser_1 LSR 1 None 12* C.0 N/A Ser_2 LSR 2 12 4 N/A N/A Ser_2 LSR 3 4 8 N/A N/A Ser_2 LSR 5 8 None** C.0 B.2 Ser_4 Router 2 C.0 C.0 C.0 Direct Eth_4 * Label appended ** Label stripped N/A = This field not parsed

  39. Now Let's Fill The LIBs Routing Table or LIB Inbound Label Outbound Label Dest. Net Next Hop I/F ID Router 1 None None C.0 2.2 Ser_1 LSR 1 None 12* C.0 N/A Ser_2 LSR 2 12 4 N/A N/A Ser_2 LSR 3 4 8 N/A N/A Ser_2 LSR 5 8 None** C.0 B.2 Ser_4 Router 2 C.0 C.0 C.0 Direct Eth_4 * Label appended ** Label stripped N/A = This field not parsed

  40. Now Let's Fill The LIBs Routing Table or LIB Inbound Label Outbound Label Dest. Net Next Hop I/F ID Router 1 None None C.0 2.2 Ser_1 LSR 1 None 12* C.0 N/A Ser_2 LSR 2 12 4 N/A N/A Ser_2 LSR 3 4 8 N/A N/A Ser_2 LSR 5 8 None** C.0 B.2 Ser_4 Router 2 C.0 C.0 C.0 Direct Eth_4 * Label appended ** Label stripped N/A = This field not parsed

  41. Label Distribution Protocols Why have one when two can be even more confusing? • LDP • RSVP Label Distribution Protocol "A set of procedures by which one Label Switched Router (LSR) informs another of the label/FEC bindings it has made" draft-ietf-mpls-arch-05.txt

  42. Label Distribution Protocols • LDP, RSVP • Maps unicast IP destinations into labels • RSVP-TE, CR-LDP • Used for Traffic Engineering and Resource Reservation • PIM • For multicast group-to-label mapping • BGP • For "extra" external label mapping

  43. Upstream vs Downstream LSR1 Downstream LSR6 Router Router Upstream LSR2 LSR3 Request LSR4 LSR1 LSR5 LSR6 MPLS Domain

  44. Label Distribution Protocol (LDP) Label distribution ensures that adjacent routers have a common view of FEC <-> label bindings Routing Table: Addr-prefix Next Hop 47.0.0.0/8 LSR3 Routing Table: Addr-prefix Next Hop 47.0.0.0/8 LSR2 LSR1 LSR3 LSR2 IP Packet 47.80.55.3 Label Information Base: Label-In FEC Label-Out XX 47.0.0.0/8 17 For 47.0.0.0/8 use label ‘17’ Label Information Base: Label-In FEC Label-Out 17 47.0.0.0/8 XX Step 2: LSR communicates binding to adjacent LSR Step 3: LSR inserts label value into forwarding base Step 1: LSR creates binding between FEC and label value Common understanding of which FEC the label is referring to! Label distribution can either piggyback on top of an existing routing protocol, or a dedicated label distribution protocol (LDP) can be created.

  45. Label Distribution - Methods Label Distribution can take place using one of two possible methods Downstream Unsolicited Label Distribution Downstream-on-Demand Label Distribution LSR2 LSR1 LSR2 LSR1 Label-FEC Binding Request for Binding • LSR2 and LSR1 are said to have an “LDP adjacency” (LSR2 being the downstream LSR) • LSR2 discovers a ‘next hop’ for a particular FEC • LSR2 generates a label for the FEC and communicates the binding to LSR1 • LSR1 inserts the binding into its forwarding tables • If LSR2 is the next hop for the FEC, LSR1 can use that label knowing that its meaning is understood Label-FEC Binding • LSR1 recognizes LSR2 as its next-hop for an FEC • A request is made to LSR2 for a binding between the FEC and a label • If LSR2 recognizes the FEC and has a next hop for it, it creates a binding and replies to LSR1 • Both LSRs then have a common understanding Both methods are supported, even in the same network at the same time For any single adjacency, LDP negotiation must agree on a common method

  46. Downstream On Demand ordered • Ingress requests label from egress Ingress Egress Label Request LSR 1 LSR 6 Label Assign Upstream Downstream Data Flow

  47. Distribution Control: Ordered v. Independent Next Hop (for FEC) MPLS path forms as associations are made between FEC next-hops and incoming and outgoing labels Incoming Label Outgoing Label Independent LSP Control Ordered LSP Control • Label-FEC binding is communicated to peers if: • - LSR is the ‘egress’ LSR to particular FEC • - label binding has been received from upstream LSR • LSP formation ‘flows’ from egress to ingress • Each LSR makes independent decision on when to generate labels and communicate them to upstream peers • Communicate label-FEC binding to peers once next-hop has been recognized • LSP is formed as incoming and outgoing labels are spliced together Definition • Labels can be exchanged with less delay • Does not depend on availability of egress node • Granularity may not be consistent across the nodes at the start • May require separate loop detection/mitigation method • Requires more delay before packets can be forwarded along the LSP • Depends on availability of egress node • Mechanism for consistent granularity and freedom from loops • Used for explicit routing and multicast Comparison Both methods are supported in the standard and can be fully interoperable

  48. INDEPENDENT MODE #14 #311 #216 #99 #311 #963 #311 D #963 #14 #612 D #462 D D D #311 #99 #5 D D D

  49. Label Retention Methods Binding for LSR5 LSR2 An LSR may receive label bindings from multiple LSRs Some bindings may come from LSRs that are not the valid next-hop for that FEC LSR1 LSR5 Binding for LSR5 LSR3 Binding for LSR5 LSR4 Conservative Label Retention Liberal Label Retention LSR2 LSR2 Label Bindings for LSR5 Label Bindings for LSR5 LSR1 LSR1 LSR3 LSR3 LSR4’s Label LSR3’s Label LSR2’s Label LSR4’s Label LSR3’s Label LSR2’s Label LSR4 LSR4 Valid Next Hop Valid Next Hop • LSR maintains bindings received from LSRs other than the valid next hop • If the next-hop changes, it may begin using these bindings immediately • May allow more rapid adaptation to routing changes • Requires an LSR to maintain many more labels • LSR only maintains bindings received from valid next hop • If the next-hop changes, binding must be requested from new next hop • Restricts adaptation to changes in routing • Fewer labels must be maintained by LSR Label Retention method trades off between label capacity and speed of adaptation to routing changes

  50. LIBERAL RETENTION MODE #216 D D #963 #14 #622 #612 D #462 D D D D #311 #422 #99 #5 D D D These labels are kept in case they are needed after a failure.

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