Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!ginger.acc.com!salt.acc.com!art
From: art@salt.acc.com (Art Berggreen)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: IP <-> X25 address mapping/conversion question
Keywords: IP, X25
Message-ID: <1989Dec7.051956.14394@ginger.acc.com>
Date: 7 Dec 89 05:19:56 GMT
References: <6539@tolerant.UUCP>
Sender: news@ginger.acc.com (USENET news)
Reply-To: art@salt.acc.com (Art Berggreen)
Distribution: usa
Organization: Advanced Computer Communications, Santa Barbara, California
Lines: 33

In article <6539@tolerant.UUCP> hahn@tolerant.UUCP (John Hahn) writes:
>
>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
  .
  .
  .
>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.

The IP over X.25 world can be split in two groups, nets that know about
IP addresses and those that don't.  For those nets that know about IP
and maintain a correspondence between IP and X.25 addresses (DDN,
Blacker I/Fs) the IP<->X.25 mappings are algorithmic.  For most of the
rest of the X.25 nets in the world there is no relationship between the
IP and X.25 addresses and address lookup tables are generally used.
The PDN working group of the IETF is looking into defining X.25 address
server protocols to avoid maintaining huge tables locally.

Art Berggreen
ACC