Telnet Proxy

Name

TELPROXY -- Telnet Proxy Server.

Description

The need may arise for a TCP/IP host on the LAN to connect first to XRPi, before making a downlink from XRPi to a target host. Using normal telnet port 23 for this purpose is not always successful, especially if the link is required to carry binary data, due to the internal end-of-line translations and Telnet command sequences which are part of the Telnet protocol.

The Telnet proxy on TCP port 2323 provides a solution to this problem, allowing 100% binary connections not only to TCP/IP targets, but also to Netrom and AX25 targets. This would typically be used by a TCP/IP-only BBS to perform FBB compressed forwarding with netrom and ax25 targets.

Upon connection to port 2323, the caller may, or otherwise, be required to answer a security challenge, according to the security criteria specified in ACCESS.SYS. The options are: no challenge, callsign only, or callsign plus password, and all of these can be made dependent on the caller's IP source address.

If a password is required, it should be located in file USERPASS.SYS.

After gaining entry, the user is presented with a short text explaining the syntax for the outgoing connection, followed by a short prompt ">". This text is read from file TELPROXY.MSG, so you may adjust it to your requirements.

The user may now issue a telnet, NetRom or ax25 downlink connect command. If the request is acceptable, XRPi responds with "Trying ...".

If the downlink is successfully made, connection is reported, then the stream becomes pure binary for the remainder of the session.

If the downlink fails to connect, an error message is sent before the uplink is terminated.

Egress Control

For TCP/IP downlinks the sysop may control which destinations are allowed (e.g. ham sites) and which are not (e.g. porn sites!). This is called "egress control" and is configured using the TELPROXY.ACL file. If the file is not present, all TCP/IP downlinking is disabled.

There is no egress control for AX25/NetRom downlinks, because it is not necessary.

Files

ACCESS.SYS controls the access requirements for the server.

TELPROXY.MSG provides an optional alternative login message.

TELPROXY.ACL controls which targets can be connected to.

USERPASS.SYS contains the user passwords, if required.

If required, these files must reside in the same directory as XRPi.exe.

See also

ACCESS.SYS(8) -- Telnet Access Control File.
TELPROXY.ACL(8) -- Telnet Proxy Egress Control File.
TELPROXY.MSG(8) -- Telnet Proxy Logon Message File
USERPASS.SYS(8) -- User Passwords File.