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From: chm@nbires.nbi.com (Paul Chmielewski)
Newsgroups: comp.protocols.tcp-ip
Subject: IP over X.25 (request for info)
Keywords: X.25, Internet Protocol, virtual circuit
Message-ID: <220@cutter.nbi.com>
Date: 2 Feb 89 17:50:47 GMT
Organization: NBI Inc., Boulder, CO.
Lines: 25


We're in the process of putting together an IP-over-X.25 package for our
4.3 derivative UNIX systems.  We currently have an intelligent communications
card (VME bus) on which we run X.25.  The UNIX kernel and networking subsystem
are pretty much straight from BSD4.3.  We plan to write a network interface
driver to interface with the X.25 code.  I'm interested in hearing from people
who have already done this or something similiar.  I'd like to hear about 
problems you ran into, what type of performance to expect, or what documentation
you found useful.  I've read RFC 877, but it doesn't seem to address all of the
issues.

I do have one specific question concerning the internet address to virtual
circuit pairings.  Is there a standard mechanism for telling the called end
of a virtual circuit what the internet address of the calling host is?  I'm
thinking that each X.25 VC or PVC will be configured as a point-to-point link.
The machine initiating the call can fairly easily map the pt-to-pt IP addresses
to the virtual circuit.  But I'm not sure how the machine accepting the call
would do this.  One possibility would be to include the initiating machines
IP address in the Call User Data Field after the protocol demultiplexing octet.
Any comments??


Paul Chmielewski		
NBI Inc., Boulder, CO		chm@nbires.UUCP or chm@nbires.NBI.COM
(303) 938-2926