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Isaicu Monica ES an I. IP/MPLS M ulti p rotocol L abel S witching. Contents. Overview Need for MPLS MPLS Basics MPLS Components and Protocols MPLS Operation Advantages and Disadvantages Evolution of MPLS References. Overview.

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Isaicu monica es an i

Isaicu Monica

ES an I

IP/MPLSMultiprotocol Label Switching


  • Overview

  • Need for MPLS

  • MPLS Basics

  • MPLS Components and Protocols

  • MPLS Operation

  • Advantages and Disadvantages

  • Evolution of MPLS

  • References


  • MPLS is a standard from the IETF for including routing information in the packets of an IP network.

  • The first IETF MPLS Working Group Meeting occurred in April of 1997

  • Widely deployed by many telcos and service providers for their Internet backbones, MPLS delivers the quality of service (QoS) required to support real-time voice and video as well as service level agreements (SLAs) that guarantee bandwidth. Large enterprises also use MPLS in their national private networks.

Need for mpls
Need for MPLS

  • IP Routing disadvantages

  • Connectionless

    - e.g. no QoS

  • Each router has to make independent forwarding decisions based on the IP-address

  • Large IP Header

    - At least 20 bytes

  • Routing in Network Layer

    - Slower than Switching

  • Usually designed to obtain shortest path

    - Do not take into account additional metrics

Need for mpls1
Need for MPLS

  • ATM (Asynchronous Transfer Mode)

  • connection oriented

    - Supports QoS

  • fast packet switching with fixed length packets (cells)

  • integration of different traffic types (voice, data, video)

    But there are also disadvantages:

  • Complex

  • Expensive

  • Not widely adopted

Need for mpls2
Need for MPLS

  • MPLS effectively pulls together the best of two different networking worlds. It allows an IP network to be operated in a controlled manner - in a similar way to legacy ATM, DTM - while maintaining the flexibility and versatility of an IP network

  • MPLS networks meet and exceed quality and reliability levels of legacy networks, while opening up a whole new world of networking flexibility.

Mpls basics
MPLS Basics

  • Multi Protocol Label Switching is arranged between Layer 2 and Layer 3

  • MPLS combines the performance and capabilities of Layer 2 (data link layer) switching with the proven scalability of Layer 3 (network layer) routing.

Mpls basics1
MPLS Basics

  • Characteristics:

    • Provides means to map IP addresses to simple, fixed-length labels

    • Remains independent of Layer-2 and Layer-3 protocols

    • Provides interfaces to existing routing protocols such as OSPF (Open Shortest path first) and RSVP (Resource reservation protocol)

    • MPLS packets can run on other Layer 2 technologies such as ATM, FR, PPP, POS, Ethernet

    • Other Layer 2 technologies can be run over an MPLS network

Mpls components and protocols
MPLS Components and Protocols

  • Label Header

  • A label is a short, fixed length, locally significant identifier which is used to identify a FEC (Forwarding Equivalence Class - a group of IP packets which are forwarded in the same manner - over the same path, with the same forwarding treatment)

  • The label which is put on a particular packet represents the FEC to which that packet is assigned.

Mpls components and protocols1
MPLS Components and Protocols

  • LER (label edge routers)

    • The entry and exit points of an MPLS network

    • Support multiple ports connected to dissimilar networks (such as frame relay, ATM, and Ethernet).

  • LSR (label switching routers)

    • High speed routers in the core on an MPLS network, that perform routing based only on the label

    • ATM switches can be used as LSRs without changing their hardware

Mpls components and protocols3
MPLS Components and Protocols

  • LSP (Label switching Path) - within an MPLS domain, a path is set up for a given packet by LSRs to travel based on a FEC

  • MPLS provides two options to set up an LSP

    • hop-by-hop routing

      • Each LSR independently selects the next hop for a given FEC. LSRs support any available routing protocols (OSPF, ISIS,BGP).

    • explicit routing

      • Is similar to source routing. The ingress LSR specifies the list of nodes through which the packet traverses.

  • The LSP setup for a FEC is unidirectional. The return traffic must take another LSP!

Mpls protocols
MPLS Protocols

  • MPLS signaling protocols are used to establish, maintain, and release label-switched paths (LSP).

  • Examples of MPLS signaling protocols include

    • Existing protocols have been extended so that label distribution can be piggybacked on them Border Gateway Protocol (BGP) and Resource Reservation Protocol (RSVP)

    • New protocols have also been defined Label Distribution Protocol (LDP) and Constraint-based Routing Label Distribution Protocol (CR-LDP)

Mpls protocols ldp
MPLS Protocols - LDP

  • LDP associates a Forwarding Equivalence Class (FEC) with each label it distributes. Two LSRs which use LDP to exchange FEC - label binding information are known as "LDP Peers", and we speak of there being an "LDP Session" between them.

  • LDP uses TCP for session communication. Use of TCP ensures that session messages are reliably delivered, and that distributed labels and state information associated with LSPs need not be refreshed periodically.

  • LDP includes a mechanism by which an LSR can discover potential LDP peers. The discovery mechanism makes it unnecessary for operators to explicitly configure each LSR with its LDP peers.

Ldp details
LDP Details

  • LDP message types:

  • discovery messages - announce and maintain the presence of an LSR in a network

  • session messages - establish, maintain, and terminate sessions between LDP peers

  • advertisement messages - create, change, and delete label mappings for FECs

  • notification messages - provide advisory information and signal error information

    All LDP messages have a common structure that uses a Type-Length-Value (TLV) encoding scheme. The Value part of a TLV - encoded object, or TLV for short, may itself contain one or more TLVs.


  • Flexibility - as a technology, MPLS imposes few restrictions on interoperability with other technologies.

  • Improves packet-forwarding performance in the network

  • Supports QoS and CoS for service differentiation - with multimedia applications gaining popularity it is essential to have QoS in place. IP based voice service needs to have more priority as it is very sensitive to delay, jitter etc. Also, video applications are used in enterprise networks as Video Conferencing and Telepresence. Such applications also need to be given priority in addition to the business critical applications. Earlier, ATM was the answer for many people to have QoS. But the things have changed and MPLS can provide ATM like QoS features. MPLS label has a 3 bit field called Traffic Class (TC) which was formerly known as EXP (Experimental) field. Core routers can provide different set of treatment for each MPLS frame based on the value of TC.


  • MPLS is used to create cost effective, private Wide Area Networks (WANs)

  • Traffic Engineering - this is a feature that every Service Provider would love to use. Mostly, SPs would be having more than one link between different routers, both for redundancy and for meeting customer requirements. The problem arises, when the bandwidth of these links are different. SP can configure the load sharing between these links using various IGP features, but that may prove to be very difficult and the model itself is not scalable. If the configurations are not properly documented, troubleshooting can be a pain. MPLS traffic Engineering can address such scenarios. The use of TE along with IGP can provide better solution.

  • It's inexpensive compared with "private" IP networks like point to point technologies.

  • As a "fully meshed" topology, MPLS assures that locations on the network can exchange data with one another (think video conferencing and VoIP).


  • An additional layer is added

  • The router has to understand MPLS

Evolution of mpls
Evolution of MPLS

  • Because of its key features MPLS has been widely adopted by enterprises for their WANs, as the most recent data from Nemertes Research (2009) indicates that around 84% of companies are now using MPLS for their WANs.

  • IETF has been working on a number of different improvements to MPLS that allows it to be applied to transport architecture, IPv6.

  • Perhaps the most important MPLS evolution will be MPLS Transport Profile (MPLS-TP), that can take advantage of features such as Quality of Service and fast reroute and put that into optical and transport networks


  • RFC 3031 - Multiprotocol Label Switching Architecture

  • Introduction to MPLS -



  • Understanding High Availability of IP and MPLS Networks