1Generalized Multiprotocol Label Switching(GMPLS)Jikai LiOverview Forms of MPLS Why MPLS? Why MPλS ? Why GMPLS? ConclusionForms of MPLS(From the IETF perspective) MPLS -- MultiProtocol Label Switching• The base technology (packet oriented) MPλS -- MultiProtocol Lambda Switching• MPLS control of lightpaths / optical trails GMPLS -- Generalized MPLS• MPLS control of Packets, Circuits, Lambdas and PortsWhy MPLS? IP Traffic Engineering– Constraint-based Routing, explicit routing Virtual Private Networks– Controllable tunneling mechanism Elimination of redundant control Ultra fast forwarding (once)2What is “Label Switching”?One of the many ways of getting from A to B:• BROADCAST: Go everywhere, stop when you get to B, never ask for directions.• HOP BY HOP ROUTING: Continually ask who’s closer to B go there, repeat … stop when you get to B. “Going to B? You’d better go to X, its on the way”.• SOURCE ROUTING: Ask for a list (that you carry with you) of places to go that eventually lead you to B. “Going to B? Go straight 5 blocks, take the next left, 6 more blocks and take a right at the lights”.Label Switching• 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#1LANE#2LANE#1 TURN RIGHT USE LANE#2A label by any other name ...There are many examples of label substitutionprotocols already in existence.• ATM - label is called VPI/VCI and travels with cell.• Frame Relay - label is called a DLCI and travels with frame.• TDM - label is called a timeslot its implied, like a lane.SO WHAT IS MPLS ? Separation of forwarding information(label)from the content of the IP header Use of single forwarding paradigm(label swapping) at the data plane to support multiple routing paradigm at the control plane Use of different technologies and link layer mechanisms to realize label swapping The concept of a forwarding hierarchy via label stacking3ROUTE AT EDGE, SWITCH IN COREIP ForwardingLABEL SWITCHINGIP ForwardingIP IP #L1 IP #L2 IP #L3 IPMPLS: HOW DOES IT WORKUDP-HelloUDP-HelloTCP-openTIMELabel requestIPLabel mapping#L2Initialization(s)BEST OF BOTH WORLDS•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!!MPLS+IPIP ATMHYBRIDMPLS Terminology LDP: Label Distribution Protocol LSP: Label Switched Path FEC: Forwarding Equivalence Class LSR: Label Switching Router LER: Label Edge Router (Useful term not in standards)4IP FORWARDING USED BY HOP-BY-HOP CONTROL47.147.247.3IP 47.1.1.1Dest Out47.1 147.2 247.3 3123Dest Out47.1 147.2 247.3 312123IP 47.1.1.1IP 47.1.1.1IP 47.1.1.1Dest Out47.1 147.2 247.3 3MPLS Label DistributionIntfInLabelInDest IntfOut3 0.40 47.1 1IntfInLabelInDest IntfOutLabelOut3 0.50 47.1 1 0.4047.147.247.3123121233IntfInDest IntfOutLabelOut3 47.1 1 0.50Mapping: 0.40Request: 47.1Mapping: 0.50Request: 47.1Label Switched Path (LSP)IntfInLabelInDest IntfOut3 0.40 47.1 1IntfInLabelInDest IntfOutLabelOut3 0.50 47.1 1 0.4047.147.247.3123121233IntfInDest IntfOutLabelOut3 47.1 1 0.50IP 47.1.1.1IP 47.1.1.1EXPLICITLY ROUTED OR ER-LSP#216#14#462- ER-LSP follows route that source chooses. In other words, the control message to establish the LSP (label request) is source routed.#972#14 #972ABCRoute={A,B,C}5EXPLICITLY ROUTED LSP ER-LSPIntfInLabelInDest IntfOut3 0.40 47.1 1IntfInLabelInDest IntfOutLabelOut3 0.50 47.1 1 0.4047.147.247.3123121233IntfInD e s t In tfOutLabelOut3 47.1.1 2 1.333 47.1 1 0.50IP 47.1.1.1IP 47.1.1.1ER 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)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• Not going to be resolved any time soon, market will probably have to resolve it.• Survival of the fittest not such a bad thing.Label EncapsulationATM FR Ethernet PPPMPLS Encapsulation is specified over various media types. Top labels may use existing format, lower label(s) use a new “shim” label format.VPI VCI DLCI “Shim Label”L2Label“Shim Label” …….IP | PAYLOAD6MPLS Link Layers• MPLS is intended to run over multiple link layers• Specifications for the following link layers currently exist:• ATM: label contained in VCI/VPI field of ATM header• Frame Relay: label contained in DLCI field in FR header• LAN: uses ‘shim’ header inserted between L2 and L3 headersTranslation between link layers types must be supportedExplicit Routing - MPLS vs. Traditional Routing• Connectionless nature of IP implies that routing is based on information in each packet header • Source routing is possible, but path must be contained in each IP header• Lengthy paths increase size of IP header, make it variable size,increase overhead• Some gigabit routers require ‘slow path’ option-based routing of IP packets • Source routing has not been widely adopted in IP and is seen as impractical• Some network operators may filter source routed packets for security reasons• MPLS’s enables the use of source routing by its connection-oriented capabilities - paths can be explicitly set up through the network - the ‘label’ can now represent the explicitly routed path• Loose and strict source routing can be supportedComparison - Hop-by-Hop vs. Explicit Routing Hop-by-Hop Routing• Distributes routing of control traffic• Builds a set of trees either fragment by fragment like a random fill, or backwards, or forwards in organized manner.• Reroute on failure impacted by convergence time of routing protocol• Existing routing protocols are destination prefix based• Difficult to perform traffic engineering, QoS-based routing Explicit Routing• Source routing of control traffic• Builds a path from source to dest• Requires manual provisioning, or automated creation mechanisms.• LSPs can be ranked so some reroute very quickly and/or backup paths may be pre-provisioned for rapid