Specifying a Tie-Breaker for Selecting CSPF Equal-Cost Paths

Constrained Shortest Path First (CSPF) may calculate multiple, equal-cost paths to the egress label Edge Router (LER). When this happens, the device chooses the path whose final node is the physical address of the destination interface. When more than one path fits this description, by default, the device chooses the path with the fewest hops. When multiple paths have this number of hops, the device chooses one of these paths at random. The user can optionally configure the device to choose the path that has either the highest available bandwidth or the lowest available bandwidth.

For example, complete the following steps for CSPF to select the path with the highest available bandwidth when choosing among equal-cost paths calculated for LSP tunnel1.

Enable the device for configuration.
```
device# configure
```
Enable the MPLS router.
```
device(config)# router mpls
```
Enable and configure the label switched path (LSP).
```
device(config-router-mpls)# lsp tunnel1
```
In this example, the LSP is configured to the LSP named tunnel1.
Select the tie breaking mode for the CSPF.
```
device(config-router-mpls-lsp-tunnel1)# tie-breaking least-fill
```
In this example, the path is selected on least-fill criteria.
The least-fill parameter causes CSPF to choose the path with the highest available bandwidth (that is, the path with the least utilized links).

Example

The following example causes CSPF to select the path with the highest available bandwidth when choosing among equal-cost paths calculated for LSP tunnel1.

device# configure terminal
device(config)# router mpls
device(config-router-mpls)# lsp tunnel1
device(config-router-mpls-lsp-tunnel1)# tie-breaking least-fill