Multi Protocol Label Switch MPLS Overview and short tutorial Credits Part of this presentation is based on James Yu lecture Many thanks and from MPLS council web site What is MPLS From MPLS Resource center MPLS stands for Multiprotocol Label Switching In an MPLS network incoming packets are assigned a label by a label edge router LER Packets are forwarded along a label switch path LSP where each label switch router LSR makes forwarding decisions based solely on the contents of the label At each hop the LSR strips off the existing label and applies a new label which tells the next hop how to forward the packet Label Switch Paths LSPs are established by network operators for a variety of purposes such as to guarantee a certain level of performance to route around network congestion or to create IP tunnels for network based virtual private networks In many ways LSPs are no different than circuit switched paths in ATM or Frame Relay networks except that they are not dependent on a particular Layer 2 technology An LSP can be established that crosses multiple Layer 2 transports such as ATM Frame Relay or Ethernet Thus one of the true promises of MPLS is the ability to create end to end circuits with specific performance characteristics across any type of transport medium eliminating the need for overlay networks or Layer 2 only control mechanisms What is MPLS OK now in plain English now please Packets enter MPLS Network at a Label Edge Router LER LER Affix a label to packet and forwards it to the MPLS network Label switches in the network at each hop makes forwarding decision solely based on label That decision is made based on a preestablished Label Switch Path LSP Labels can be integrated with existing L2 info such as DLCI or ATM VCs Diagram in class MPLS Motivation Original drivers towards label switching Designed to make routers faster ATM switches were faster than routers Fixed length label lookup faster than longest match used by IP routing Allow a device to do the same job as a router with performance of ATM switch Enabled IP ATM integration Mapping of IP to ATM had become very complex hence simplify by replacing ATM signalling protocols with IP control protocols MPLS Motivation Growth and evolution of the Internet The need to evolve routing algorithm The need for advanced forwarding algorithm routing vs forwarding switching routing flexibility forwarding price performance Can we forward switch IP packets Allow speed of L2 switching at L3 Router makes L3 forwarding decision based on a single field similar to L2 forwarding Sppppppeeeeed Some MPLS Benefits Traffic Engineering the ability to set the path traffic will take through the network and the ability to set performance characteristics for a class of traffic VPNs using MPLS service providers can create IP tunnels throughout their network without the need for encryption or end user applications Layer 2 Transport New standards being defined by the IETF s PWE3 and PPVPN working groups allow service providers to carry Layer 2 services including Ethernet Frame Relay and ATM over an IP MPLS core Elimination of Multiple Layers Typically most carrier networks employ an overlay model where SONET SDH is deployed at Layer 1 ATM is used at Layer 2 and IP is used at Layer 3 Using MPLS carriers can migrate many of the functions of the SONET SDH and ATM control plane to Layer 3 thereby simplifying network management and network complexity Eventually carrier networks may be able to migrate away from SONET SDH and ATM all together which means elimination of ATM s inherent cell tax in carrying IP traffic MPLS History IP over ATM IP Switching by Ipsilon Cell Switching Router CSR by Toshiba Tag switching by Cisco Aggregate Route based IP Switching IBM IETF MPLS http www ietf org html charters mpls charter html RFC3031 MPLS Architecture RFC2702 Requirements for TE over MPLS RFC3036 LDP Specification MPLS and ISO model MPLS is a layer 2 5 protocol Applications TCP UDP IP MPLS PPP FR ATM Ethernet MP S DWDM Physical When a layer is added no modification is needed on the existing layers Label Switching What is it Goal sending a packet from A to B We can do it in a broadcast way We can use source routing where the source determines the path How do we do it on the Internet today Hop by hop routing continue asking who is closer to B at every stop hop Using Label on the network This is not new ATM VPI VCI Frame Relay DLCI X 25 LCI logical Channel Identifier TDM the time slot Circuit Identification Code Ethernet switching Q do you see any commonality of these labels Label Substitution swapping Label A1 Label B1 Label A2 Label B2 Label A3 Label B3 Label A4 Label B4 MPLS A protocol to establish an end to end path from source to the destination A hop by hop forwarding mechanism Use labels to set up the path Require a protocol to set up the labels along the path It builds a connection oriented service on the IP network Terminology LSR Routers that support MPLS are called Label Switch Router LER LSR at the edge of the network is called Label Edge Router a k a Edge LSR Ingress LER is responsible for adding labels to unlabeled IP packets Egress LER is responsible for removing the labels Label Switch Path LSP the path defined by the labels through LSRs between two LERs Label Forwarding Information Base LFIB a forwarding table mapping between labels to outgoing interfaces Forward Equivalent Class FEC All IP packets follow the same path on the MPLS network and receive the same treatment at each node How does it work remove label at the egress LER Add label at the ingress LER LSR LER IP IP IP Routing L1 LSR IP Label Switching L2 LER IP Label Switching L3 IP Routing IP MPLS Operation Label Path R1 R2 R3 R4 Label Forwarding Information Base LFIB Router Incomin g Label Incoming Interface Destinatio n Network FEC Outgoin g Interfac e Outgoin g Label R1 E0 172 16 1 0 S1 6 R2 6 S0 172 16 1 0 S2 11 R3 11 S0 172 16 1 0 S3 7 R4 7 S1 172 26 1 0 E0 Q create LFIB for R4 R3 R2 R1 MPLS process Label Switch Path Routing Protocol FEC FEC Label Swapping Classification Label assignment FEC Label removal LFIB LFIB Layer 2 Layer 2 Layer 2 Layer 1 Layer 1 Layer 1 Ingress Node Core Node Egress Node LFIB Label Encapsulation Label information can be carried in a packet in a variety of ways A small shim label header inserted between the Layer 2 and network layer headers As part of the Layer 2 header if the Layer 2 header provides adequate semantics such as ATM As part of the network layer