Solaris 10 route add on specific interface

The route command has the -p option, in OpenSolaris and I believe Solaris 10 as well. From man route:

 -p             Make changes to the network route tables per-
                sistent across system restarts. The operation
                is applied  to  the  network  routing  tables
                first  and, if successful, is then applied to
                the list  of  saved  routes  used  at  system
                startup.  In determining whether an operation
                was successful, a failure to add a route that
                already  exists  or to delete a route that is
                not in the routing table is ignored. Particu-
                lar  care  should be taken when using host or
                network  names  in  persistent   routes,   as
                network-based  name  resolution  services are
                not available at the time routes are added at
                startup.

I believe it writes them to the /etc/inet/static_routes file if they are applied successfully.

C:\Documents and Settings\Administrator>route -p add x.x.x.x mask 255.255.255.255 192.168.96.199 The route addition failed: Either the interface index is wrong or the gateway does not lie on the same network as the interface. Check the IP Address Table for the machine.

Your host is on the 192.168.12.0 subnet but the gateway address for the route you're trying to add is on the 192.168.96.x subnet, which is not local to your host. The gateway address has to be local to (on the same subnet as) your host.