VMS Help TN3270, Qualifiers, /PORT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /PORT=n

    Optional. Default: 23.

    Remote port to which you want your TELNET/TN3270 process to
    connect. Specify only if you are connecting to a host that does
    not use the standard TELNET port.