Srlg Limitations; Soft-Preemption - Cisco ASR 9000 Series Configuration Manual

Soft-Preemption

with the protected link. Setting the admin weight consists of adding a penalty metric to make using the link
less desirable.
For more information about Weighted-SRLG auto-backup path computation, see Implementing MPLS Traffic
Engineering chapter in the Cisco ASR 9000 Series Aggregation Services Router MPLS Configuration Guide.
For more information about Weighted-SRLG auto-backup path computation, see MPLS Traffic Engineering
Commands chapter in the Cisco ASR 9000 Series Aggregation Services Router MPLS Command Reference.
Related Topics
Configuring the SRLG Values of Each Link that has a Shared Risk with Another Link, on page 212
Creating an Explicit Path With Exclude SRLG, on page 214
Using Explicit Path With Exclude SRLG, on page 216
Creating a Link Protection on Backup Tunnel with SRLG Constraint, on page 218
Creating a Node Protection on Backup Tunnel with SRLG Constraint, on page 221
Configure the MPLS-TE Shared Risk Link Groups: Example, on page 259

SRLG Limitations

There are few limitations to the configured SRLG feature:
• The exclude-address and exclude-srlg options are not allowed in the IP explicit path strict-address
• Whenever SRLG values are modified after tunnels are signalled, they are verified dynamically in the
Related Topics
Configuring the SRLG Values of Each Link that has a Shared Risk with Another Link, on page 212
Creating an Explicit Path With Exclude SRLG, on page 214
Using Explicit Path With Exclude SRLG, on page 216
Creating a Link Protection on Backup Tunnel with SRLG Constraint, on page 218
Creating a Node Protection on Backup Tunnel with SRLG Constraint, on page 221
Configure the MPLS-TE Shared Risk Link Groups: Example, on page 259
Soft-Preemption
MPLS-TE preemption consists of freeing the resources of an established LSP, and assigning them to a new
LSP. The freeing of resources causes a traffic disruption to the LSP that is being preempted. Soft preemption
is an extension to the RSVP-TE protocol to minimize and even eliminate such traffic disruption over the
preempted LSP.
The soft-preemption feature attempts to preempt the LSPs in a graceful manner to minimize or eliminate
traffic loss. However, the link might be over-subscribed for a period of time.
In a network that implements soft preemption, zero traffic loss is achieved in this manner:
• When signaling a new LSP, the ingress router indicates to all the intermediate nodes that the existing
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network.
next path verification cycle.
LSP is to be softly preempted, in case its resources are needed and is to be reassigned.
Implementing MPLS Traffic Engineering
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