Specifying a source address for an LSP

To specify a source IP address of 10.2.3.4 for LSP tunnel1, complete the following steps.

Enable the device for configuration.
```
device# configure
```
Enable the MPLS router.
```
device(config)# router mpls
```
Assign the signaled label switched path (LSP).
```
device(config-router-mpls)# lsp tunnel1
```
In this example, the specified LSP is tunnel1.
Specify the source IP address.
```
device(config-router-mpls-lsp-tunnel1)# from 10.2.3.4
```
In this example, the specified source address is 10.2.3.4.

The following examples show IP address 10.2.3.4 being assigned as the source IP address for LSP tunnel1.

device# configure 
device(config)# router mpls
device(config-router-mpls)# lsp tunnel1
device(config-router-mpls-lsp-tunnel1)# from 10.2.3.4

The from command specifies the source IP address to be carried in RSVP Path messages for the LSP. This command is optional. When the from command is specified, then the address is always carried in RSVP path messages as the source IP address for the LSP. When the from command is not specified, and when the LSP is enabled, the device dynamically determines the source IP address of the LSP (using the device's first loopback as the source IP address).

Note

A loopback interface must be configured for RSVP to use it as source IP address when the from command is not specified.

The IP address specified in the from command affects only the IP address carried in the RSVP path messages for the LSP. It does not affect the outgoing interface (and thus the actual path) that the path messages are sent out.