The DRS_EXTENSIONS structure defines a concrete type for capabilities information used in version negotiation.

 typedef struct {
   [range(1,10000)] DWORD cb;
   [size_is(cb)] BYTE rgb[];
 } DRS_EXTENSIONS;

cb: The size, in bytes, of the rgb array.

rgb: To RPC, this field is a string of cb bytes. It is interpreted by the client and the server as the first cb bytes of a DRS_EXTENSIONS_INT structure that follow the cb field of that structure. The fields of the DRS_EXTENSIONS_INT structure are in little-endian byte order. Since both DRS_EXTENSIONS and DRS_EXTENSIONS_INT begin with a DWORD cb, a field in DRS_EXTENSIONS_INT is at the same offset in DRS_EXTENSIONS as it is in DRS_EXTENSIONS_INT.