IV. Features ================ This software, and x.25 in general, has a few nice features. If you receive an x.25 call from somewhere, the NUA ("Network User Address") of the caller is being transmitted to you. This works pretty much like Caller-ID, with the exception that the caller can't prevent it from being transmitted, and he usually can't fake the address he is calling from. Of course he can call through a couple of systems, and you would just see the NUA of the last system he calls you from. This feature can easily be used to accept or reject calls from certain NUAs/systems or whole countries. Many systems like banks just allow certain NUAs to call them, just the ones that they know. You could also give different access to different people: people from country A may login to your system, country B may just write you a mail, all other countries are forced into chat and the NUA of CERT is being rejected and received a "nice" goodbye message. Of course you will also keep a logfile (and 99% of the systems you call will have a logfile with YOUR call and the calls you might place using its pad). This logfile usually contains the NUA that calls you (or that is being called), the programs that are being executed, the userid of the caller, duration, reason for termination and more. Another interesting feature is the 'Call User Data' (CUD). The caller may transmit up to 16 bytes (default is 4 bytes) to your host before he establishes an x.25 connection. In these bytes he may send you a Service Request. The default CUD is 01/00/00/00 and means 'interactive login'. You may define any CUD you want and just accept calls that use that certain CUD - it would work like a system password then. Many systems may also have a service request that allows the caller to execute commands on that host remotely, without supplying any additional password (be aware of this!) For more technical information about x.25 read one of the articles in the previous issues of Phrack. I am glad that Phrack is still covering x.25 with plenty of interesting articles after all these years! telnet> open pythia.csi.forth.gr 2600 Trying 139.91.1.1 ... Connected to pythia.csi.forth.gr. Escape character is '^]'. Welcome to Sectec Direct. Please hold the line. :) Email me for information or accounts, or just send me love letters :) sec@g386bsd.first.gmd.de. by Seven Up (damiano @ irc)