MPLS Multiprotocol Label Switching 20000515 Topics n Introduction

MPLS: Multi-protocol Label Switching 2000/05/15

Topics n Introduction n MPLS protocols n n RSVP-TE/CR-LDP MPLS applications n n History and motivation MPLS mechanisms VPNSs, traffic engineering, restoration Generalized MPLS 2000/05/15 2

WHY MPLS ? n Ultra fast forwarding n n IP Traffic Engineering n n Constraint-based routing Virtual Private Networks n n Use switching instead of routing Controllable tunneling mechanism Protection and restoration 3

IP Forwarding Table 3 3 1 1 47. 1. *. * 2 2 1 47. 2. *. * 47. 3. *. * 3 2 2000/05/15 4

Hop-by-Hop IP Forwarding 1 47. 1 3 1 IP 47. 1. 1. 1 2 IP 47. 1. 1. 1 1 47. 2 47. 3 3 2 IP 47. 1. 1. 1 2000/05/15 5

Routing Lookup Control CPU Switch fabric I/F 10 Gbps Prefix 9. *. *. * 9. 1. *. * 9. 2. *. * 9. 1. 1. * 9. 2. 1. * 9. 1. 1. 1 9. 1. 1. 2 9. 2. 1. 1 Next Hop 14. 1. 2. 1 67. 1. 2. 2 71. 1. 2. 3 113. 1. 2. 1 71. 1. 2. 3 14. 1. 2. 1 71. 1. 2. 3 Interface 2 4 6 8 8 6 20 M packets/sec n n Longest prefix match is (was) expensive. Label matching is much less expensive. 2000/05/15 6

MPLS Labels Request: 47. 1 3 st: que 1 1 Re 47. 3 3 2 2000/05/15 47. 1 pp Ma 0. ing: 50 2 1 47. 1 3 2 Mapping: 0. 40 47. 2 7

Label Switched Path IP 47. 1. 1. 1 1 47. 1 3 3 1 1 47. 3 3 2 2 47. 2 2 IP 47. 1. 1. 1 2000/05/15 8

Forwarding Equivalence Classes LER LSR LER LSP IP 1 IP 2 IP 1 #L 1 IP 1 #L 2 IP 1 #L 3 IP 2 #L 1 IP 2 #L 2 IP 2 #L 3 IP 2 Packets are destined for different address prefixes, but can be mapped to common path n n n 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. L 3 look-up), in MPLS it is only done once at the network ingress 2000/05/15 9

MPLS Terminology n n n LDP: Label Distribution Protocol LSP: Label Switched Path FEC: Forwarding Equivalence Class LSR: Label Switching Router LER: Label Edge Router 2000/05/15 10

Label Distribution Methods Downstream Label Distribution LSR 1 LSR 2 Label-FEC Binding • LSR 2 discovers a ‘next hop’ for a particular FEC • LSR 2 generates a label for the FEC and communicates the binding to LSR 1 Downstream-on-Demand Label Distribution LSR 1 LSR 2 Request for Binding Label-FEC Binding • LSR 1 recognizes LSR 2 as its next-hop for an FEC • LSR 1 inserts the binding into its forwarding tables • A request is made to LSR 2 for a binding between the FEC and a label • If LSR 2 is the next hop for the FEC, LSR 1 can use that label knowing that its meaning is understood • If LSR 2 recognizes the FEC and has a next hop for it, it creates a binding and replies to LSR 1 • Both LSRs then have a common understanding Both methods are supported, even in the same network at the same time 2000/05/15 11

Distribution Control Incoming Label Independent LSP Control Definition Comparison • Each LSR makes independent decision on when to generate labels and communicate them to upstream peers • Communicate label-FEC binding to peers once nexthop has been recognized • LSP is formed as incoming and outgoing labels are spliced together • 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 Next Hop (for FEC) Outgoing Label 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 • 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 Both methods are supported in the standard and can be fully interoperable 2000/05/15 12

Label Retention Methods Conservative Label Retention Liberal Label Retention Label Bindings for LSR 5 LSR 2 LSR 1 Label Bindings for LSR 5 LSR 3 LSR 4’s Label LSR 3’s Label LSR 2’s Label Valid Next Hop LSR 4 • 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 2 LSR 1 LSR 3 LSR 4’s Label LSR 3’s Label LSR 2’s Label Valid Next Hop LSR 4 • 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 2000/05/15 13

Label Encapsulation L 2 ATM FR Label VPI VCI DLCI Ethernet PPP “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. 2000/05/15 14

Label Format Label 20 bits n n n Exp 3 bits Stack 1 bit TTL 8 bits Exp field used to identify the class of service Stack bit is used identify the last label in the label stack TTL field is used as a time-to-live counter. Special processing rules are used to mimic IP TTL semantics. 2000/05/15 15

Label Distribution Protocols n n Label Distribution Protocol (LDP) Constraint-based Routing LDP (CR-LDP) Extensions to RSVP Extensions to BGP 2000/05/15 16

LDP: Label Distribution Protocol Label distribution ensures that adjacent routers have a common view of FEC <-> label bindings Routing Table: Addr-prefix 47. 0. 0. 0/8 Next Hop LSR 2 Next Hop LSR 3 LSR 1 IP Packet LSR 3 LSR 2 47. 80. 55. 3 Label Information Base: Label-In FEC Label-Out XX 47. 0. 0. 0/8 17 Step 3: LSR inserts label value into forwarding base 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 1: LSR creates binding between FEC and label value Common understanding of which FEC the label is referring to! 2000/05/15 17

LDP: Basic Characteristics n n Provides LSR discovery mechanisms to enable LSR peers to find each other and establish communication Defines four classes of messages n n n DISCOVERY: deals with finding neighboring LSRs ADJACENCY: deals with initialization, keep alive, and shutdown of sessions LABEL ADVERTISEMENT: deals with label binding advertisements, request, withdrawal, and release NOTIFICATION: deals with advisory information and signal error information Runs over TCP for reliable delivery of messages, except for discovery, which uses UDP and IP multicast Designed to be extensible, using messages specified as TLVs (type, value, length) encoded objects. 2000/05/15 18

LDP Messages n n n INITIALIZATION KEEPALIVE LABEL MAPPING LABEL WITHDRAWAL LABEL RELEASE LABEL REQUEST 2000/05/15 19

Explicitly Routed LSP IP 47. 1. 1. 1 1 47. 1 3 3 1 1 47. 3 3 2 2 47. 2 2 IP 47. 1. 1. 1 2000/05/15 20

ER LSP - Advantages n Operator has routing flexibility n n n policy-based, Qo. S-based Can use routes other than shortest path Can compute routes based on constraints in exactly the same manner as ATM based on distributed topology database. (traffic engineering) 2000/05/15 21

ER LSP - discord! n n n Two signaling options proposed in the standards: CR-LDP, RSVP extensions: CR-LDP = LDP + Explicit Route RSVP ext = Traditional RSVP + Explicit Route +Scalability Extensions Market will probably have to resolve it Survival of the fittest not such a bad thing. 2000/05/15 22

MPLS and Qo. S in IP Network n n Integrated Services Differentiated Services 2000/05/15 23

Integrated Services Internet n Applications specify traffic and service specs n n n Two classes of service defined n n n Tspec: traffic specs including peak rate, maximum packet size, burst size, and mean rate Rspec: service spec, specifically service rate Guaranteed service: satisfies hard guarantees on bandwidth and delay Controlled load service: provides service similar to that in “unloaded network” RSVP was extended to RSVP-TE support signaling n RSVP was further extend to add MPLS support 2000/05/15 24

Differentiated Services Internet n IP packets carry 6 -bit service code points (DSCP) n n Potentially support 64 -different classes of services Routers map DSCP to per-hop-behavior (PHB) n n PHBs can be standard or local Standard PHBs include n n Default: No special treatment or best effort Expedited forwarding (EF): Low delay and loss Assured forwarding (AF): Multiple classes, each class with multiple drop priorities LSRs don’t sort based on IP headers, hence DSCPs need to be mapped to EXP field in MPLS shim header n n n Exp field is only 3 -bit wide – can support only 8 DSCPs/PHBs Labels can be used if more than 8 PHBs need to be supported Same approach can be used for link layers which do not use Shim headers, e. g. ATM 2000/05/15 25

Traffic Engineering with RSVP PATH {Tspec} Sender RESV {Rspec} 2000/05/15 RESV {Rspec} PATH {Tspec} RESV {Rspec} Receiver 26

Label Distribution with RSVP-TE PATH {Tspec} Sender RESV {Rspec} PATH {Tspec} 2000/05/15 RESV {Rspec} {Label = 10} RESV {Rspec} {Label = 5} PATH {Tspec} RESV {Rspec} 27

MPLS Protection n n End-to-end protection Fast node and link reroute 2000/05/15 28

MPLS Protection End-to-end Path Protection F Primary LSP E A D B C Backup LSP Backup and primary LSPs should be route diverse 2000/05/15 29

MPLS Protection Fast Reroute Detour to avoid CD Detour to avoid AB LSR A LSR D LSR C Detour to avoid BC n LSR E Detour to avoid DE Detour around node or link failures n n Detour to avoid link DE LSR F Example LSP shown traverses (A, B, C, D, E, F) Each detour avoids n n Immediate downstream node & link towards it Except for last detour: only avoids link DE 2000/05/15 30

Detour Merging Detour to avoid AB Merged detour to avoid AB and BC Detour to avoid BC LSR A n n LSR B LSR C LSR F LSR D LSR E Reduces state maintained Improves resource utilization 2000/05/15 31

MPLS Protection Types n 1+1: Backup LSP established in advance, resources dedicated, data simultaneously sent on both primary and backup n n n Switchover performed only by egress LSR Fastest, but most resource intensive 1: 1 : Same as 1+1 with the difference that data is not sent on the backup n n n Requires failure notification to the ingress LSR to start transmitting on backup Notification may be send to egress also Resources in the backup may be used by other traffic n Low priority traffic (e. g. , plain IP traffic), shared by other backup paths 2000/05/15 32

MPLS VPN: The Problem Customer 1 Site 1 Provider Network 10. 2/16 Customer 1 Site 2 10. 1/16 10. 2/16 Customer 2 Site 2 10. 1/16 Customer 2 Site 1 10. 3/16 Customer 2 Site 3 2000/05/15 Customer 1 Site 3 10. 3/16 33

MPLS VPN: The Model Customer 1 Site 1 10. 1/16 10. 2/16 Customer 1 Virtual Network 10. 2/16 10. 1/16 Customer 2 Site 2 Customer 2 Virtual Network Customer 2 Site 1 10. 3/16 Customer 2 Site 3 2000/05/15 Customer 1 Site 2 Customer 1 Site 3 10. 3/16 34

MPLS VPN: The Solution MPLS LSP Customer 1 Site 1 10. 2/16 Customer 1 Site 2 VRF 1 10. 1/16 VRF 1 10. 2/16 VRF 2 Customer 2 Site 2 VRF 2 10. 1/16 VRF 1 Customer 2 Site 1 VRF 2 MPLS LSP 10. 3/16 Customer 2 Site 3 2000/05/15 Customer 1 Site 3 10. 3/16 35

Unified Control Plane IP Network E-NNI UNI Optical Network Optical subnet IP Network I-NNI E-NNI ATM Network Optical subnet E-NNI ATM Network ATM ATM Network 2000/05/15 UNI IP Network UNI - User-to-Network Interface I-NNI - Internal Network-to-Network Interface E-NNI - External Network-to-Network Interface 36

GMPLS: Generalized MPLS PSC Cloud n n n LSC Cloud FSC Cloud GMPLS Handles Nodes With Diverse Capabilities. n n TDM Cloud Packet Switch Capable (PSC) Time Division Multiplexing Capable (TDM) Lambda Switch Capable (LSC) Fiber Switch Capable (FSC) Each Node Is Treated As an MPLS Label-switching Router (LSR) Lightpaths/TDM Circuits Are Considered Similar to Label-Switched Paths (LSPs) n Selection of s and OXC ports are considered similar to selection of labels 2000/05/15 37