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Chapter Objectives

Chapter Objectives. After completing this chapter you will be able to: Describe the concept of MPLS List some advantages of MPLS Describe the structure of an MPLS network Describe how a Label Switched Path (LSP) is set up. Multiprotocol Label Switching (MPLS).

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Chapter Objectives

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  1. Chapter Objectives After completing this chapter you will be able to: • Describe the concept of MPLS • List some advantages of MPLS • Describe the structure of an MPLS network • Describe how a Label Switched Path (LSP) is set up

  2. Multiprotocol Label Switching (MPLS) • MPLS is an Internet Engineering Task Force (IETF) forwarding standard • Concept: • Packets entering the network are analysed and put into a forward equivalence class (FEC) • Forward equivalence classes are mapped to connections through the network • The packet is labelled according to which path it should take through the network • Packet is transferred though the network by switching on the label

  3. MPLS Implementation MPLS can be implemented as: • A layer 3 solution • Label is an extra piece of data appended onto the IP header • An IP over Frame Relay solution • Label is the Data Link Control Identifier (DLCI) • An IP over ATM solution • Label is the VPI/VCI value

  4. ...And replace the ATM software with new software that understands IP. Keep the ATM hardware... IP Addressing IP Routing Label Distribution Protocol (LDP) UNI Signaling PNNI Signaling PNNI Routing ATM Addressing The Label Distribution Protocol can be thought of as 'IP signaling'. MPLS IP over ATM

  5. MPLS Network Architecture Label Switching Router (LSR) deployed in the core of the network to perform high speed label switching. Is an ATM switch running MPLS software. Label Edge Router (LER) deployed at the edge of the network for connectivity to user networks. Is a router with an ATM interface running MPLS software.

  6. Label Distribution Protocol (LDP) LDP is responsible for setting up ATM connections. These connections (LSPs) are set up in response to topology information Network B

  7. Forward Equivalence Class (FEC) • An FEC is defined as a group of layer three (network layer) packets that can be forwarded in the same manner. • Forward Equivalence Classes (FECs) are mapped directly to LSPs. • An FEC may comprise traffic to a particular destination or it may be more specific, comprising traffic to a particular destination with distinct service requirements. • Facilitates complex mappings that would otherwise be impossible.

  8. MPLS Advantages • Simplified Forwarding • No process intensive forwarding decision • Efficient Explicit Routing • Advanced routing such as QoS routing • Service Differentiation • Since FEC decision made at edge more complex mappings can be made • Multiple Services • ATM is a multiservice infrastructure

  9. MPLS Scalability • Previous IP over ATM methods make use of either: • a full mesh 'n- squared' overlay of virtual circuits between n ATM-attached routers • a partial mesh of VCs between routers • a partial mesh of VCs, plus the use of NHRP to facilitate on demand cut-through SVCs • MPLS scales better because MPLS nodes only have to peer with those nodes they are directly connected to • PVC method requires all edge nodes to peer with all other edge nodes

  10. Do We Still Need L3 Forwarding? • Yes • Why? • Labels will get close to the destination network, but we need to uniquely identify the destination • Security, for packet filtering at firewalls • For forwarding at the initial router when the hosts don’t support MPLS • For forwarding at the intradomain routing protocol’s border

  11. Methods of Label Assignment • Topology Driven • Amount of control information is proportional to the number of destinations • Flow Driven • Amount of control information is proportional to the number of individual flows

  12. Merging LSPs Two channels One channel

  13. 32 bits Type 14 bits Length 16 bits U F Value (variable length) Type Length Values (TLVs)

  14. LDP Message Types • Discovery messages • Session messages • Advertisement messages • Notification messages

  15. Interface Destination LIB (Labels) LIB (Labels) LIB (Labels) A VP=0, VC=33 1 A VP=0, VC=45 1 A VP=0, VC=75 2 from connection VP=0, VC=45 2 from connection VP=0, VC=75 2 RIP RIP RIP RIP OSPF OSPF OSPF OSPF LDP LDP LDP LDP Layer 3 Layer 2 Connection through the ATM switch Network A Network C Network B Network D VP=0, VC=33 VP=0, VC=45 VP=0, VC=75 Request label for destination A LER 2 LSR 2 LSR 1 LER 1 Request label for destination A Request label for destination A Label is VP=0, VC=33 Label is VP=0, VC=45 Label is VP=0, VC=75 LER LER LSR LSR Establishing an LSP

  16. LinkFailure • LDP sends keepalive messages to its peers • If none received session is cancelled • Either LDP or routing protocols notice a failed link • All LSPs using this link will be signalled down • Routing tables will be consulted to determine alternative routes

  17. Loops • Concerned here with L2 (ATM) loops • Loop survival • Loop prevention • Loop detection

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