Route preferences are used to select which route is installed in the forwarding table when several protocols calculate routes to the same destination. The route with the lowest preference value is selected. For more information about route preferences, see Route Preferences Overview.
By default, Level 1 IS-IS internal routes have a preference value of 15, Level 2 IS-IS internal routes have a preference of 18, Level 1 IS-IS external routes have a preference of 160, and Level 2 external routes have a preference of 165. To change the preference values, include the preference statement (for internal routes) or the external-preference statement:
For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.
The preference value can range from 0 through 4,294,967,295 (232 – 1).