The JUNOS software provides support for alternate and tiebreaker preferences, and some of the routing protocols, including BGP and label switching, use these additional preferences. With these protocols, you can specify a primary route preference, preference, and a secondary preference, preference2, that is used as a tiebreaker. You can also mark route preferences with additional route tiebreaker information by specifying a color, color, and a tiebreaker color, color2.
The software uses a 4-byte value to represent the route preference value. When using the preference value to select an active route, the software first compares the primary route preference values, choosing the route with the lowest value. If there is a tie and a secondary preference has been configured, the software compares the secondary preference values, choosing the route with the lowest value. The secondary preference values must be included in a set for the preference values to be considered.