Library /sys$common/syshlp/ncphelp.hlb SET, MODULE, X25-SERVER, KNOWN DESTINATIONS, EXTENSION VALUE hex-string  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Provides a value for the called address extension facility. This
 value  is compared with the address extension in the incoming
 call (after  merging as described in EXTENSION MASK). By default
 no extension value is used.