Starting in the Solaris 10 release, the NFS client no longer uses an excessive number of UDP ports. Previously, NFS transfers over UDP used a separate UDP port for each outstanding request. Now, by default, the NFS client uses only one UDP reserved port. However, this support is configurable. If the use of more simultaneous ports would increase system performance through increased scalability, then the system can be configured to use more ports. This capability also mirrors the NFS over TCP support, which has had this kind of configurability since its inception. For more information, refer to the Oracle Solaris Tunable Parameters Reference Manual.
NFS version 4 does not use UDP. If you mount a file system with the proto=udp option, then NFS version 3 is used instead of version 4.