Juniper JUNOSE, Configuration Manual

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sender, it does so by periodically sending targeted hellos to the initiating LSR. The
exchange of targeted hellos constitutes a hello adjacency for the two LSRs.
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 on page 209
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MPLS Label Distribution Protocols on page 229
MPLS Traffic Engineering
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
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MPLS Traffic Engineering
JUNOSe 11.0.x BGP and MPLS Configuration Guide