Telebahn is an emulation of an X.25-based Public Data Network – a loose collection of systems that accept X.25 calls through XoT (X.25-over-TCP).
One of them is a Cisco 1760 router at Dunelab, which you can call at 471041. It also acts as a gateway (X.25 switch) to the other two Cisco1760's (which are 471042 and 471043 respectively).
You can call 471041 and use IOS telnet to access dn42. Vice versa, you can telnet from dn42 to labrtr1.nullroute.dn42 and use the IOS pad command to make X.25 calls to Telebahn.
Cisco1760-top#pad hansvax
Translating "hansvax.sym"...domain server (10.147.10.53) [OK]
Trying 23000200...Open
Welcome to EUGENE, a VAX 4000/105A running VAX/VMS 5.5-2H4
Please log in as GUEST if you don't have an account and want to have a look.
Log in as NEW to create an account for yourself.
Username: GUEST
Welcome to VAX/VMS V5.5-2H4
You can use the SEND command to chat for now. PHONE is always available,
and HELP is your friend. Enjoy!
Last interactive login on Saturday, 4-JAN-2025 13:06
Last non-interactive login on Saturday, 24-JUN-2023 18:31
<Welcome, TELEBAHN.471041>
$ dir
Directory SYS$SYSDEVICE:[GUEST]
$MAIN.TPU$JOURNAL;5 $MAIN.TPU$JOURNAL;4 $MAIN.TPU$JOURNAL;3 $MAIN.TPU$JOURNAL;2
$MAIN.TPU$JOURNAL;1 LOGIN.COM;2 LOGIN.COM;1 NETSERVER.LOG;1
NOTES$NOTEBOOK.NOTE;1 TEST.DIR;1
Total of 10 files.
$ log
GUEST logged out at 23-JAN-2025 11:51:43.53
[Connection to hansvax closed by foreign host]
Cisco1760-top#
To set up outbound XoT routing on Cisco IOS, use:
service pad to-xot x25 routing x25 route ^471 xot dns x25.nullroute.lt x25 route ^(...)(...) xot dns \2.\1.x25.org x25 route ^ clear
The first route (optional) specifically handles the 471 prefix, while the second covers all other Telebahn members (yes, that's a regexp). Finally a catch-all route gives an explicit "Destination unreachable" result for everything else – the IOS implicit default is actually to route all such calls through the first X.25-capable interface.
You should also need to define a custom X.25 profile, both to select the appropriate X.25 version and other parameters, and also to set your own X.25 "caller" address as XoT calls aren't associated with any physical interface (normally the caller address would be taken from the outbound interface).
x25 profile TELEBAHN dxe x25 version 1988 x25 modulo 128 x25 address ######## x25 win 7 x25 wout 7 x25 ips 1024 x25 ops 1024 x25 subscribe packetsize permit 128 1024 x25 subscribe windowsize permit 2 15 ! access-list 10 remark Match all XoT hosts access-list 10 permit any no xot access-group 10 xot access-group 10 profile TELEBAHN
In theory X.25 should allow negotiation of certain parameters such as window size (win/wout and packet size (ips/ops) but sometimes incompatible parameters make the call fail outright; these should work for most systems. Remember that changes to the profile are only applied once you unassign and re-assign it via xot access-group.
Once everything is set up, you can use pad to make a call from IOS EXEC prompt, or x28 to enter the arcane X.28 "standard PAD user interface". (This example shows off Cisco support for X25 records in DNS.)