Avaya Configuring MPLS Services Manuel d'utilisateur télécharger pdf (Page 18)

Configuring MPLS Services

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305754-A Rev 00

MPLS General Information

Multiprotocol Label Switching (MPLS) is an emerging Internet Engineering Task

Force (IETF) standard that is currently in draft form. Its primary goal is to provide

a standardized solution that supersedes existing proprietary solutions for

integrating label-swapping and forwarding with network layer routing. MPLS

works in an environment where traditional network layer routing protocols (for

example, OSPF and BGP) are used to maintain the routing topology and

forwarding information base (FIB) for each router.

In connectionless networks (those using connectionless network layer protocols),

as a packet travels from one hop to another, each router must determine where to

forward the packet based on the individual packet header. This decision process

can be broken down into two major tasks: classifying a set of packets as part of a

forwarding equivalence class (FEC) and mapping each FEC to a next hop.

By classifying a set of packets as part of an FEC, the router uses the same

forwarding criteria for each packet. All packets that belong to a particular FEC

and that travel from a particular node follow the same path. This group of packets

is called a “stream.” A packet stream is a group of packets that follows the same

path to a destination. In a conventional IP network, each router hop examines each

packet to determine its destination.

Using MPLS, the examination of the packet is done only once. The first router

assigns a label that defines the specific packet stream. Each intervening router

then forwards packets based on the fixed-length labels. Labels reside in the label

information base (LIB), which contains both inbound and outbound labels

associated with inbound and outbound interfaces.

Looking up a label is faster than interpreting the destination of an individual

packet and routing data based on that destination. By assigning labels to packets

or packet streams, the transmission speed of your network increases.

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Avaya Configuring MPLS Services Manuel d'utilisateur Page 18