Juniper JUNOSE, Configuration Manual

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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 path that is not as good as the failed path. You can have MPLS periodically
search—according to a specified schedule—for a path better than the alternate by
configuring the reoptimization timer. For example, you might configure MPLS to
search for a better path every 10 minutes; if it finds a better path, it switches.
On the other hand, you might be concerned about route flapping. If a path goes
down and then comes back up, perhaps it will continue to do so. In this case, you
might not ever want to go back to a path that goes down. To accomplish this, you
can configure reoptimization to never occur.
When you do not want the initial path to change—that is, when you want to pin the
route—you can disable reoptimization globally by setting the timer to 0. Alternatively,
you can disable reoptimization on a per-tunnel basis by using the
lockdown option
with the tunnel mpls path-option command. LSP paths are always pinned until the
next reoptimization.
Finally, you can manually force an immediate reoptimization. See MPLS Global
Configuration Tasks in Configuring MPLS in the JUNOSe BGP and MPLS Configuration
Guide for information about configuring reoptimization.
Methods for Configuring RSVP-TE Tunnels
You can use either of the following methods to configure RSVP-TE tunnels:
■
Configure individual tunnels with the interface tunnel mpls: tunnelName
command.
■
Configure multiple tunnels with the same set of parameters with the mpls
tunnels profile command.
Tracking Resources for MPLS Traffic Engineering
MPLS traffic engineering uses admission control to keep track of resource information.
Admission control has an accounting feature that ensures that requests are not
accepted when the router does not have sufficient resources to accommodate them.
Currently, bandwidth (BW) and bandwidth-related information are the only resources
tracked and used for traffic engineering. Admission control determines whether a
setup request can be honored for an MPLS LSP with traffic parameters.
Admission control provides bandwidth information to the IGP protocols, ISIS and
OSPF. As new LSPs are created, the available bandwidth decreases. The IGPs can
subsequently advertise this information and use it for SPF calculations to determine
paths that satisfy the traffic requirements. You can configure readvertisement to
occur periodically or when the change crosses some threshold.
MPLS Traffic Engineering
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Chapter 2: MPLS Overview