The route version is the earlier of the two site version numbers of the source and destination Replication Servers of the route. After you upgrade the source and destination Replication Servers on either end of a route and also set their site versions to a higher Replication Server version, you need to upgrade the route.
Upgrading the route allows the Replication Servers to exchange information about newer software features. Upgrading a route rematerializes the data in the system tables in the RSSD and makes information associated with new features available to a newly upgraded Replication Server. After upgrading, new types of information that were not previously allowed can be exchanged.
Replication Server version 11.5 or later uses route version information to determine which feature set you can use with the route and which data to propagate to other sites. If the route version is lower than the earliest site version, you must perform a route upgrade. For example, information necessary for version 15.5 features is not propagated to other sites until the corresponding route versions are upgraded to 1550.
After you upgrade to Replication Server 15.6 and set the site version to 1550, you must upgrade each route for which this Replication Server is a source or destination, and the site versions of the source and destination are at 1550 or later.
How you upgrade routes depends on how you use Replication Server, and whether you are using a mixed-version system.