Overview Of Mpls-Te Features; How Mpls-Te Works - Cisco NCS 5500 Series Configuration Manual

Overview of MPLS-TE Features

Overview of MPLS-TE Features
In MPLS traffic engineering, IGP extensions flood the TE information across the network. Once the IGP
distributes the link attributes and bandwidth information, the headend router calculates the best path from
head to tail for the MPLS-TE tunnel. This path can also be configured explicitly. Once the path is calculated,
RSVP-TE is used to set up the TE LSP (Labeled Switch Path).
To forward the traffic, you can configure autoroute, forward adjacency, or static routing. The autoroute feature
announces the routes assigned by the tailend router and its downstream routes to the routing table of the
headend router and the tunnel is considered as a directly connected link to the tunnel.
If forward adjacency is enabled, MPLS-TE tunnel is advertised as a link in an IGP network with the link's
cost associated with it. Routers outside of the TE domain can see the TE tunnel and use it to compute the
shortest path for routing traffic throughout the network.
MPLS-TE provides protection mechanism known as fast reroute to minimize packet loss during a failure. For
fast reroute, you need to create back up tunnels. The autotunnel backup feature enables a router to dynamically
build backup tunnels when they are needed instead of pre-configuring each backup tunnel and then assign the
backup tunnel to the protected interfaces.
DiffServ Aware Traffic Engineering (DS-TE) enables you to configure multiple bandwidth constraints on an
MPLS-enabled interface to support various classes of service (CoS). These bandwidth constraints can be
treated differently based on the requirement for the traffic class using that constraint.
The MPLS traffic engineering auto-tunnel mesh feature allows you to set up full mesh of TE tunnels
automatically with a minimal set of MPLS traffic engineering configurations. The MPLS-TE auto bandwidth
feature allows you to automatically adjusts bandwidth based on traffic patterns without traffic disruption.
The MPLS-TE interarea tunneling feature allows you to establish TE tunnels spanning multiple Interior
Gateway Protocol (IGP) areas and levels, thus eliminating the requirement that headend and tailend routers
should reside in a single area.
For detailed information about MPLS-TE features, see

How MPLS-TE Works

MPLS-TE automatically establishes and maintains label switched paths (LSPs) across the backbone by using
RSVP. The path that an LSP uses is determined by the LSP resource requirements and network resources,
such as bandwidth. Available resources are flooded by extensions to a link state based Interior Gateway
Protocol (IGP). MPLS-TE tunnels are calculated at the LSP headend router, based on a fit between the required
and available resources (constraint-based routing). The IGP automatically routes the traffic to these LSPs.
Typically, a packet crossing the MPLS-TE backbone travels on a single LSP that connects the ingress point
to the egress point.
The following sections describe the components of MPLS-TE:
Tunnel Interfaces
From a Layer 2 standpoint, an MPLS tunnel interface represents the headend of an LSP. It is configured with
a set of resource requirements, such as bandwidth and media requirements, and priority. From a Layer 3
standpoint, an LSP tunnel interface is the headend of a unidirectional virtual link to the tunnel destination.
MPLS Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
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Implementing MPLS Traffic Engineering
MPLS-TE Features - Details, on page 51.