X.25 to TCP/IP

X.25 to TCP/IP

Post by Thoma » Wed, 18 Dec 2002 18:34:33



Hi,

Does anyone know of an existing solution to convert X.25 to TCP/IP? By that
I mean taking the payload out of one and putting it into the other one (as
opposed to X.25 over TCP/IP or vice versa).

So far I have found programs that use telnet to send and receive commands
over X.25, but I really want just a pure converter. The ability to open up
X.25 connection when a TCP/IP connection request is received (and vice versa
again) would be great.

I believe the cisco IOS software does this, but can anyone tell me for sure?

Thanks in advance,
Tom

 
 
 

X.25 to TCP/IP

Post by Kevin Doole » Thu, 19 Dec 2002 11:11:11


Cisco has a feature called XOT (X.25 Over TCP) that does what you seem to
want.  It is a tunneling protocol that simply takes an X.25 connection from
a serial port on the router, encapsulated it in TCP/IP (I believe it's on
TCP port 1998) and sends it to another router where the X.25 is pulled out
of TCP packet and delivered to another serial port. It won't convert, say,
an X.25 terminal session into a TELNET session.  But if you want to do that,
then chances are you need a PAD, and you can also configure PAD
functionality on a Cisco router if you like.

I've used XOT in some large networks where it allowed us eliminate the need
for a parallel low-speed network just for the X.25.  You can configure some
relatively sophisticated routing tables that map X.121 addresses to IP
addresses.  It works very well, and you can even do some clever tricks like
rewriting X.25 addresses as you route them (which breaks some applications
that check X.121 addresses), and CUGs.

The one caveat is that you can route an X.25 call from serial port to serial
port, from serial to a remote IP address, from an incoming XOT session to a
serial port ... but *not* from IP to IP.  This has huge implications for
your routing table design, because just about everybody decides that it
would be cool to put a single route on all of their remotes, pointing to a
central distribution router that will then find the right destination
device.  But I'll save you the grief... it doesn't work that way.  You have
to route directly to the destination router.

On the router you configure something like this:

!
x25 routing
!
interface Serial1
 description An X.25 DCE device
 encapsulation x25 dce
 clockrate 19200
!

interface Serial2
 description An X.25 DTE device
 encapsulation x25 dte
 clockrate 19200
!
interface Serial3
 description An X.25 DCE device with some non-default parameters
 encapsulation x25 dce
 x25 win 7
 x25 wout 7
 x25 ips 256
 x25 ops 256
 clockrate 19200
 lapb k 4
!
x25 route 10000001 interface Serial1
x25 route 10000002 interface Serial2
x25 route 10000003 interface Serial3
x25 route 20000001 xot 10.1.1.1 10.2.1.1
x25 route 20000002 xot 10.1.2.3 10.2.2.3
!

Note that you can set up multiple IP destinations in your XOT routes.  The
router will try all of these destinations in order.  This is extremely
useful for high availability configurations.  A good trick I've done a few
times is to configure the destination IP addresses on the destination serial
ports with either a /30 or /32 mask.  That way, if the serial port goes
down, the route drops out of your routing table, and you can dynamically
switch any new calls over to the other port.  It won't dynamically switch
existing calls, but it's better than nothing.

The "x25 route" command also takes regular expressions.  So you can create
some very simple routing entries.  For example, if you have 8 X.25 serial
ports on one router, and they all look like "1230001", "1230002", "1230003",
etc, you can just create a single routing entry that looks like this:

x25 route 123000. xot 10.1.2.4

or you might even be able to get away with something like:

x25 route ^123 xot 10.1.2.4

XOT is documented in RFC 1613.   As far as going the other way, there is an
RFC on encapsulating IP in X.25, which is documented in RFC 877.

Hope this helps,

Kevin Dooley
http://www.manageablenetworks.com
Author: Designing Large-Scale LANs (O'Reilly, 2002)


Quote:> Hi,

> Does anyone know of an existing solution to convert X.25 to TCP/IP? By
that
> I mean taking the payload out of one and putting it into the other one (as
> opposed to X.25 over TCP/IP or vice versa).

> So far I have found programs that use telnet to send and receive commands
> over X.25, but I really want just a pure converter. The ability to open up
> X.25 connection when a TCP/IP connection request is received (and vice
versa
> again) would be great.

> I believe the cisco IOS software does this, but can anyone tell me for
sure?

> Thanks in advance,
> Tom


 
 
 

X.25 to TCP/IP

Post by James Knot » Fri, 20 Dec 2002 08:34:21



> Hi,

> Does anyone know of an existing solution to convert X.25 to TCP/IP? By
> that I mean taking the payload out of one and putting it into the other
> one (as opposed to X.25 over TCP/IP or vice versa).

> So far I have found programs that use telnet to send and receive commands
> over X.25, but I really want just a pure converter. The ability to open up
> X.25 connection when a TCP/IP connection request is received (and vice
> versa again) would be great.

> I believe the cisco IOS software does this, but can anyone tell me for
> sure?

I believe there's some info on the Linux Documentation Project, about AX.25,
an amateur radio implementation of X.25.  You might find some help in it.

--

Fundamentalism is fundamentally wrong.


james.knott.

 
 
 

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