MPLS: Multi-protocol Label Switching

2000/05/152 Topics Introduction History and motivation MPLS mechanisms MPLS protocols RSVP-TE/CR-LDP MPLS applications VPNSs, traffic engineering, restoration Generalized MPLS

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

2000/05/154 IP Forwarding Table 47.1.*.* 47.2.*.* 47.3.*.*

2000/05/155 Hop-by-Hop IP Forwarding IP

2000/05/156 Routing Lookup Longest prefix match is (was) expensive. Label matching is much less expensive. 10 Gbps 20M packets/sec Switch fabric Control CPU I/F 9.*.*.* *.* *.* * * PrefixNext Hop Interface

2000/05/157 MPLS Labels Mapping: 0.40 Request: 47.1 Mapping: 0.50 Request: 47.1

2000/05/158 Label Switched Path IP

2000/05/159 Forwarding Equivalence Classes 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 Packets are destined for different address prefixes, but can be mapped to common path IP1 IP2 IP1 IP2 LSR LER LSP IP1#L1 IP2#L1 IP1#L2 IP2#L2 IP1#L3 IP2#L3

2000/05/1510 MPLS Terminology LDP: Label Distribution Protocol LSP: Label Switched Path FEC: Forwarding Equivalence Class LSR: Label Switching Router LER: Label Edge Router

2000/05/1511 Label Distribution Methods LSR1 LSR2 Downstream Label Distribution Label-FEC Binding 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 LSR1 LSR2 Downstream-on-Demand Label Distribution 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 Request for Binding Both methods are supported, even in the same network at the same time

2000/05/1512 Distribution Control Independent LSP Control Ordered LSP Control Next Hop (for FEC) Outgoing Label Incoming Label 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 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 Definition Comparison 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 Both methods are supported in the standard and can be fully interoperable

2000/05/1513 Label Retention Methods Liberal Label Retention Conservative Label Retention LSR1 LSR2 LSR3 LSR4 Label Bindings for LSR5 Valid Next Hop LSR4’s Label LSR3’s Label LSR2’s Label LSR1 LSR2 LSR3 LSR4 Label Bindings for LSR5 Valid Next Hop LSR4’s Label LSR3’s Label LSR2’s Label 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

2000/05/1514 Label Encapsulation ATMFREthernetPPP MPLS Encapsulation is specified over various media types. Top labels may use existing format, lower label(s) use a new “shim” label format. VPIVCIDLCI“Shim Label” L2 Label “Shim Label” ……. IP | PAYLOAD

2000/05/1515 Label Format 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. Label 20 bits Exp 3 bits Stack 1 bit TTL 8 bits

2000/05/1516 Label Distribution Protocols Label Distribution Protocol (LDP) Constraint-based Routing LDP (CR-LDP) Extensions to RSVP Extensions to BGP

2000/05/1517 LDP:Label Distribution Protocol Label distribution ensures that adjacent routers have a common view of FEC label bindings Routing Table: Addr-prefix Next Hop /8 LSR2 Routing Table: Addr-prefix Next Hop /8 LSR2 LSR1 LSR2 LSR3 IP Packet Routing Table: Addr-prefix Next Hop /8 LSR3 Routing Table: Addr-prefix Next Hop /8 LSR3 For /8 use label ‘17’ Label Information Base: Label-In FEC Label-Out /8 XX Label Information Base: Label-In FEC Label-Out /8 XX Label Information Base: Label-In FEC Label-Out XX /8 17 Label Information Base: Label-In FEC Label-Out XX /8 17 Step 1: LSR creates binding between FEC and label value Step 2: LSR communicates binding to adjacent LSR Step 3: LSR inserts label value into forwarding base Common understanding of which FEC the label is referring to!

2000/05/1518 LDP: Basic Characteristics Provides LSR discovery mechanisms to enable LSR peers to find each other and establish communication Defines four classes of messages 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 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.

2000/05/1519 LDP Messages INITIALIZATION KEEPALIVE LABEL MAPPING LABEL WITHDRAWAL LABEL RELEASE LABEL REQUEST

2000/05/ IP Explicitly Routed LSP

2000/05/1521 ER LSP - Advantages Operator has routing flexibility policy-based, QoS-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)

2000/05/1522 ER LSP - discord! 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.

2000/05/1523 MPLS and QoS in IP Network Integrated Services Differentiated Services

2000/05/1524 Integrated Services Internet Applications specify traffic and service specs Tspec: traffic specs including peak rate, maximum packet size, burst size, and mean rate Rspec: service spec, specifically service rate Two classes of service defined 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 RSVP was further extend to add MPLS support

2000/05/1525 Differentiated Services Internet IP packets carry 6-bit service code points (DSCP) Potentially support 64-different classes of services Routers map DSCP to per-hop-behavior (PHB) PHBs can be standard or local Standard PHBs include 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 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

2000/05/1526 Traffic Engineering with RSVP Sender Receiver PATH {Tspec} RESV {Rspec} PATH {Tspec} RESV {Rspec}

2000/05/1527 Label Distribution with RSVP-TE PATH {Tspec} RESV {Rspec} {Label = 5} RESV {Rspec} {Label = 10} Sender PATH {Tspec} RESV {Rspec} PATH {Tspec} RESV {Rspec}

2000/05/1528 MPLS Protection End-to-end protection Fast node and link reroute

2000/05/1529 MPLS Protection End-to-end Path Protection A C B D E F Backup LSP Primary LSP Backup and primary LSPs should be route diverse

2000/05/1530 MPLS Protection Fast Reroute LSR A LSR F LSR E LSR D LSR C LSR B Detour to avoid AB Detour to avoid BC Detour to avoid CD Detour to avoid DE Detour to avoid link DE Detour around node or link failures Example LSP shown traverses (A, B, C, D, E, F) Each detour avoids Immediate downstream node & link towards it Except for last detour: only avoids link DE

2000/05/1531 Detour Merging LSR A LSR F LSR E LSR D LSR C LSR B Detour to avoid AB Detour to avoid BC Merged detour to avoid AB and BC Reduces state maintained Improves resource utilization

2000/05/1532 MPLS Protection Types 1+1: Backup LSP established in advance, resources dedicated, data simultaneously sent on both primary and backup 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 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 Low priority traffic (e.g., plain IP traffic), shared by other backup paths

2000/05/1533 MPLS VPN: The Problem 10.1/ / /16 Provider Network Customer 1 Site 1 Customer 1 Site 2 Customer 1 Site 3 Customer 2 Site 3 Customer 2 Site 1 Customer 2 Site 2

2000/05/1534 MPLS VPN: The Model 10.1/ / /16 Customer 1 Site 1 Customer 2 Site 1 Customer 2 Site 3 Customer 1 Site 3 Customer 2 Site 2 Customer 1 Site 2 Customer 1 Virtual Network Customer 2 Virtual Network

2000/05/1535 MPLS VPN: The Solution 10.1/ / /16 Customer 1 Site 1 Customer 1 Site 2 Customer 1 Site 3 Customer 2 Site 3 Customer 2 Site 1 Customer 2 Site 2 VRF 1 VRF 2 MPLS LSP

2000/05/1536 Unified Control Plane UNI - User-to-Network Interface I-NNI - Internal Network-to-Network Interface E-NNI - External Network-to-Network Interface Optical Network Optical subnet Optical subnet Optical subnet UNI E-NNI I-NNI ATM Network IP Network ATM Network IP Network ATM Network

2000/05/1537 GMPLS: Generalized MPLS GMPLS Handles Nodes With Diverse Capabilities. 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) Selection of s and OXC ports are considered similar to selection of labels FSC Cloud LSC Cloud TDM Cloud PSC Cloud