Specifying the Primary Path for an LSP

The primary path is the route that packets generally travel when going through an LSP.

The user can specify a user-defined path or no path at all. Once the LSP is enabled, the ingress LER attempts to signal the other LSRs in the path so that resources can be allocated to the LSP. When the user does not specify a primary path, the path used in the LSP is the shortest path to the egress LER, as determined from standard IP routing methods, or CSPF when it is enabled.

In the following example, to specify the sf_to_sj path as the primary path for LSP tunnel1, complete the following steps.

Enable the device for configuration.
```
device# configure
```
Enable the MPLS router.
```
device(config)# router mpls
```
Enable and configure the specified label switched path (LSP).
```
device(config-router-mpls)# lsp tunnel1
```
In this example, the specified LSP is tunnel1.
Configure the primary path.
```
device(config-router-mpls-lsp-tunnel1)# primary-path sf_to_sj
```
In this example, the primary path is defined as sf_to_sj.

Example

The following example configures the primary path as sf_to_sj for LSP tunnel1.

device# configure
device(config)# router mpls
device(config-router-mpls)# lsp tunnel1
device(config-router-mpls-lsp-tunnel1)# primary-path sf_to_sj