LSP Preemption
You can develop a preemption strategy whereby a new LSP can claim resources from
an existing LSP. Each tunnel can be configured with a setup priority and a hold priority.
Priority levels range from 0 (highest priority) through 7 (lowest priority).
If traffic engineering admission control determines that there are insufficient resources
to accept a request to set up a new LSP, the setup priority is evaluated against the hold
priority of existing LSPs. An LSP with a hold priority lower than the setup priority of the
new LSP can be preempted. The existing LSP is terminated to make room (free resources)
for the new LSP. You must assign priorities according to network policies to prevent
resource poaching and LSP thrashing.
Related Topics See Configuring MPLS on page 275, for information about displaying information related
to traffic-engineering resources
•
Topology-Driven LSPs Overview
Topology-driven LSPs are implemented for best-effort, hop-by-hop routing. In
topology-driven LSP mode, LDP automatically sets up LSPs for IGP, direct, and static
routes, subject to filtering by access-lists. JunosE supports downstream-unsolicited LDP
using the platform label space.
If you use the topology-driven LSP mode to forward plain IP packets, use the ldp
ip-forwarding command to place LSPs into the IP routing table for forwarding plain IP
traffic.
You can use the mpls ldp advertise-labels command to limit the number of routes for
which labels are advertised. In most cases, you can issue mpls ldp advertise-labels
host-only.
LDP over RSVP-TE
If you are running RSVP-TE in the core, LDP can tunnel through the core by stacking an
LDP LSP over an RSVP-TE LSP, as shown in Figure 58 on page 256. With LDP over RSVP-TE,
LDP establishes targeted sessions among the LDP routers at the edge of the RSVP core.
From the perspective of the LDP LSP, the RSVP-TE core is a single hop.
255Copyright © 2010, Juniper Networks, Inc.
Chapter 3: MPLS Overview
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