Library /sys$common/syshlp/ncphelp.hlb SET, EXECUTOR, BUFFER SIZE number  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Specifies in bytes the size of the receive buffers, thereby
 controlling the maximum size of NSP message segments that can be
 received and forwarded.  The size includes protocol overhead down to
 and including the End Communication layer, but does not include the
 Data Link layer overhead.  This buffer size applies to all circuits
 known to the executor.  The default value is equal to the value of the
 SEGMENT BUFFER SIZE, if specified; otherwise the default is 576.

 The value of the BUFFER SIZE parameter must be greater than or equal
 to the value of the SEGMENT BUFFER SIZE parameter.  The two values are
 normally equal but may differ to permit the network manager to alter
 buffer size on all nodes without interruption of service.  Refer to
 the DECnet for OpenVMS Networking Manual for information about how to
 modify buffer sizes.