Assigning Version Numbers

Most new protocols evolve into more efficient, stable, and mature protocols. As a program evolves, a new version number (vers parameter) is assigned. The version number identifies which version of the protocol the caller is using. The first implementation of a remote program is usually designated as version number 1 (or a similar form).

Version numbers make it possible to use old and new protocols through the same server. See Using Multiple Program Versions Example.

Just as remote program protocols may change over several versions, the actual RPC message protocol can also change. Therefore, the call message also contains the RPC version number. In the second version of the RPC protocol specification, the version number is always 2.