Foundry NetIron M2404C and M2404F Metro Access Switches
Configuring MPLS and H-VPLS (Rev. 03)
Multiprotocol Label Switching
© 2008 Foundry Networks, Inc
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Multiprotocol Label Switching
Multiprotocol Label Switching (MPLS), used mainly for service provider core networks and large
enterprise networks, is an architecture that overcomes many of the shortcomings of IP-based
networks. It provides an easy way to engineer traffic, manage bandwidth, and bring Quality of
Service (QoS) to IP networks.
MPLS is capable of building Virtual Circuits (VCs) across IP networks. VCs can be regarded as
tunnels for different kinds of packets, transported via the MPLS network. One of the most common
applications of VCs is the Virtual Private LAN Service (VPLS). In the MPLS world each path
from the entry of the MPLS cloud (ingress) to some exit point of the cloud (egress) is called Label
Switched Path (LSP). A specific label corresponds to each LSP. It is attached to the packets at the
ingress point.
MPLS nodes attach labels to packets and forward them across LSPs. The incoming labels are used
as an index into a label information base, which specifies the next hop interface for the packet, as
well as the new label to be attached to the packet. Nodes in the core MPLS network do not need to
examine packets and perform next-hop routing tasks. The label is the only information that
determines which path a packet should take.
MPLS supports traffic engineering to provide traffic prioritization and QoS. Multiple paths can be
defined between two endpoints to achieve load balancing and provide backup in case of a line
failure. This is similar to using metrics in IP routing to force traffic in one direction or another.
Overview
Figure 1: MPLS Cloud
An MPLS network is typically a large group of core switches that are distributed over a wide
geographic area. MPLS may also be used in metropolitan area networks. Periphery non-MPLS
networks are attached to the edges of the MPLS network via Label Edge Routers (LERs), while the
core is built of Label Switching Routers (LSRs). LERs are edge devices that connect with external
non-MPLS networks; LSRs are core devices that perform MPLS switching (see
Figure 1
). An LSP
is the path that a packet will follow inside the MPLS cloud once a label is attached to it at the