Targeted hello values are configured globally with the mpls ldp targeted-hello holdtime,
mpls ldp targeted-hello interval, mpls ldp targeted-hello receive list, and mpls ldp
targeted hello send list commands.
Related Topics MPLS Label Switching and Packet Forwarding Overview on page 218•
• MPLS Label Distribution Protocols Overview on page 238
MPLS Traffic Engineering Overview
MPLS traffic engineering (TE) is the ability to establish LSPs according to particular
criteria (constraints) in order to meet specific traffic requirements rather than relying on
the path chosen by the conventional IGP. The constraint-based IGP examines the available
network resources and calculates the shortest path for a particular tunnel that has the
resources required by that tunnel. Traffic engineering enables you to make the best use
of your network resources by reducing overuse and underuse of certain links.
Constraint-based routing (CR) makes traffic engineering possible by considering resource
requirements and resource availability rather than merely the shortest path calculations.
Constraints are determined at the edge of the network and include criteria such as required
values for bandwidth or required explicit paths. You can use RSVP-TE as the label
distribution protocol for traffic engineering. The IGP propagates resource information
throughout its network. RSVP-TE employs downstream-on-demand, ordered control
for label mapping and distribution.
Explicit routing specifies a list or group of nodes (hops) that must be used in setting up
the tunnels. CR explicit paths can be strict or loose. Strict paths specify an exact physical
path, including every physical node. Loose paths include hops that have local flexibility;
the hop can be a traditional interface, an autonomous system, or an LSP.
LSP Backup
You can configure multiple LSPs to the same destination. By configuring different tunnel
metrics for these LSPs, you can force a ranking or priority of use for the LSPs. In this
scenario, all the configured LSPs are up and active. If the LSP in use develops problems
and goes down, traffic is diverted to the LSP having the next best metric.
Path Option
You can configure multiple paths for an LSP with the tunnel mpls path-option command.
Each path option has an identifying number; the lower the number the higher the
preference for that path option. In this scenario, only a single LSP is up and active at a
time. If the path option currently in use by an LSP goes down, MPLS tries to reroute the
tunnel using the path option with the next highest preference. In certain circumstances—for
example, when a tunnel is preempted by another—MPLS first attempts to reroute the
tunnel with the current path option.
Reoptimization
You can use the traffic-engineering reoptimization capability to ensure that the best path
is being used. Suppose the current path goes down and MPLS switches to an alternate
Copyright © 2010, Juniper Networks, Inc.252
JunosE 11.2.x BGP and MPLS Configuration Guide
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