Enable IS-IS LSPs with TE Extensions for MPLS Interfaces

When an MPLS-enabled device receives an IS-IS TE LSP, it stores the traffic engineering information in its Traffic Engineering Database (TED). The device uses information in the TED when performing calculations to determine a path for an LSP.

Information related to traffic engineering is carried in IS-IS traffic engineering LSPs. IS-IS TE LSPs have special extensions that contain information about an interface‘s administrative group memberships, IPv4 interface address, IPv4 neighbor address, maximum link bandwidth, reservable link bandwidth, unreserved bandwidth, and default traffic engineering metrics.

The user can configure the device to send out IS-IS TE LSPs to selected MPLS-enabled interfaces. To do this, complete the following steps.

Configure the device.
```
device# configure
```
Enable the MPLS router.
```
device(config)# router mpls
```
Enable MPLS policy configuration.
```
device(config-router-mpls)# policy
```
Enable IGP for advertising traffic engineering. In this example IS-IS traffic engineering for level 1 is selected.
```
device(config-router-mpls-policy)# traffic-engineering isis level-1
```
The level-1 option enables LSPs with TE extensions for the IS-IS level-1 domain. The level-2 option enables LSPs with TE extensions for the IS-IS level-2 domain.

Example

The following example configures the device to send out IS-IS-TE LSPs for all of its MPLS-enabled interface.

device# configure
device(config)# router mpls
device(config-router-mpls)# policy
device(config-router-mpls-policy)# traffic-engineering isis level-1

By default, the device does not send out IS-IS LSPs with TE extensions for its MPLS-enabled interfaces. Since information in the TED is used to make path selections using CSPF, and information in the TED comes from OSPF-TE LSAs or IS-IS LSPs with TE extensions, the user must enable the device to send out OSPF-TE LSAs or IS-IS LSPs with TE extensions when the user wants CSPF to perform constraint-based path selection.