Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!usc!wuarchive!decwrl!nsc!voder!tolerant!hahn
From: hahn@tolerant.UUCP (John Hahn)
Newsgroups: comp.protocols.tcp-ip
Subject: IP <-> X25 address mapping/conversion question
Keywords: IP, X25
Message-ID: <6539@tolerant.UUCP>
Date: 6 Dec 89 02:42:50 GMT
Distribution: usa
Organization: Tolerant Software Inc., San Jose CA
Lines: 38


I am looking for some information on the Internet Ip-addr to X25
address mapping/conversion issue. I always assumed that in order to
have TCP-IP run on top of X25 the addresses have to be mapped since
Internet and X25 address spaces were incompatible. However when I
was investigating the BSD4.3 implementation on the VAX it looks as if
there is an address conversion based on some DDN spec. 
The conversion routine goes as follows.

/*	@(#)if_ddn.c	7.1 (Berkeley) 6/5/86 */
	Copyright (c) 1985 by Advanced Computer Communications
*									*
*	NOTE: Although IF-11/X25 was designed to accept ASCII coded	*
static boolean convert_ip_addr(ip_addr, x25addr)
struct in_addr ip_addr;
u_char x25addr[];
  {
    register int temp;
    union {
	struct in_addr ip;
	struct {	 /*   (assumes Class A network number) */
	    u_char s_net;
	    u_char s_host;
	    u_char s_lh;
	    u_char s_impno;
	} imp;
    } imp_addr;

    if (imp_addr.imp.s_host < 64)	/* Physical:  0000 0 IIIHH00 [SS] */
      {					/*   s_impno -> III, s_host -> HH */
    else			/* Logical:   0000 1 RRRRR00 [SS]	*/
      {				/*   s_host * 256 + s_impno -> RRRRR	*/
Which then brings up the question if this is useable with the 
Public Data Networks (i.e. Telenet, Tymnet, Transpac ..etc)? 
Is this only for some DDN private networks and one must resort to 
mapping the address for use with the PDN's?

Thanks in advance for those who can enlighten me.