Cisco ASR 900 Series User Manual

Link IP Address: 102.103.1.1
Designated Router: 102.103.1.2
TE metric: 1
IGP metric: 1
SRLGs: 10 20 30 40 50
Physical Bandwidth: 1000000 kbits/sec
Res. Global BW: 200000 kbits/sec
Res. Sub BW: 120000 kbits/sec
Downstream::
Flex LSP Non-Revertive 1:1 Path Protection
Currently, MPLS-TE path protection is triggered every time a fail is detected on a working path (assuming a
protect path is configured and available). Once the fail is resolved, TE switches back traffic to the working
path. The process of switching back the traffic to the working path is done in a make-before-break fashion
but it still does not guarantee that traffic jitter or delay is not introduced (due to different path lengths between
working and protect paths). This jitter is not desirable in delay-intolerant applications like Circuit Emulation
(CEM).
In Cisco IOS XE Everest 16.5.1, TE no longer switches back to the working path when the working path is
restored. Instead, the protected path continues to be the working path. This behavior is achieved by configuring
a specific attribute, [non-revertive], to the protecting path-options.
However, if the non-revertive option is configured, TE switches back to the working path.
This is the sequence of actions for MPLS TE when the non-revertive protect path is configured:
1
Detects failure on the current path.
2
Switches to the protect path. The protect path now becomes the active non-revertive path (that is, the path
carrying traffic).
3
Signals a new path and marks it as pending. This new pending path must be diverse from the active path,
only if the diverse option is configured on the protect path option.
4
Re-optimizes this pending path periodically (but at the same time ensures this is diverse from the active
non-revertive protect path).
5
Switches over to the pending path, if the active path fails [traffic is wrapped]. Marks pending path as active
path. Re-signals a protect path for the new active path.
6
You can force traffic to a pending path by running the command mpls traffic-eng switch non-revertive.
In this case, the pending path becomes the current active path and the non-revertive path is re-signaled as
a protect path for the new current path.
Configuring Flex LSP Non-Revertive Path Protection
The following command is used to configure the non-revertive path protection:
[no] tunnel mpls traffic-eng path-option protect [preference] {diverse | explicit {identifier
[id] | name [name]} | list {identifier [id] | name [name]}} [non-revertive]
The following sample configuration illustrates a co-routed Flex LSP enabled with the non-revertive option:
MPLS Basic Configuration Guide, Cisco IOS XE Everest 16.5.1 (Cisco ASR 900 Series)
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Flex LSP Overview
Flex LSP Non-Revertive 1:1 Path Protection

Cisco ASR 900 Series Specifications

General

Brand	Cisco
Model	ASR 900 Series
Category	Network Router
Language	English