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Full Discussion: Telnet
Special Forums IP Networking Telnet Post 302893312 by Corona688 on Tuesday 18th of March 2014 12:36:12 PM
Old 03-18-2014
Telnet is an insecure way to login to something, not because it's "telnet", but because it's a raw network connection which sends pure text. In other words, it's not telnet that's insecure, it's the way you use it. It's just a raw network connection. That it's totally raw allows it to connect to HTTP, FTP, POP3, etc with equal ease. It can't tell the difference. It's just a socket() call.

ssh isn't useful as a diagnostic tool the way telnet is because it has a complex protocol. You can telnet into FTP, HTTP, and POP3 servers to see what's going on, and it won't care that one sends 'HELLO', another sends '404 not found', another prints 'LOGIN', or whatever -- it just dumps it all to the screen as-is. SSH will expect a key exchange or something and crash out when given anything else.

FTP via telnet is no safer than FTP with an FTP client, also. It's not some weird property of telnet which makes telnet insecure -- it's that it's a raw network connection which anything can peek on. FTP is also usually raw. (sftp is not ftp, it's ssh -- it just looks like it from the client point of view. ftps, which is pretty rare, actually is FTP, tunneled in an SSH connection.)

Another useful and common utility is netcat, usually "nc", which is a raw connection like telnet but contains many more options for automatic use.

Last edited by Corona688; 03-18-2014 at 01:49 PM..
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cyclades-ser-cli(8)													       cyclades-ser-cli(8)

NAME
cyclades-ser-cli Serial Port Interface for Cyclades Terminal Servers SYNOPSIS
cyclades-ser-cli [options] devname rasname physport DESCRIPTION
The cyclades-ser-cli program connects a Unix device file 'devname' to a physical port 'physport' of a Cyclades Terminal Server 'rasname'. cyclades-ser-cli provides the I/O interface between the device file and the physical port, running as an 'user-mode device driver'. If 'physport' is assigned to 0, then 'rasname' is used as the IP address on an IP-based serial port addressing. OPTIONS
cyclades-ser-cli may be started with the following options: -u ptyiosize Sets the internal device I/O size to ptyiosize (maximum 4096 bytes, default 1024 bytes) -n netiosize Sets the internal socket I/O size to netiosize (maximum 512 bytes, default 128 bytes) -i retrydelay Delay in seconds between connection requests (default: 60) -r retries Number of connection request retries before exiting. (default: infinity) -s Use the Socket Server protocol for talking to the server, this means just piping all the data down a TCP connection with no control information, so it's impossible to change the port speed etc. The default is to use the RFC2217 protocol. -m modem handling The default is 0 which means to check DCD state, 1 means to ignore DCD. -c close mode Last close handling; the default is 0 which means to hangup the modem, 1 means not to hangup. -p start port TCP base port of servers at terminal server side (defaults: 31000 for Socket server, 30000 for Remote Telnet Server). Note: if 'physport' is assigned to zero, this option has no effect, the Telnet Server standard port (23) is used. -d debug level The default is debug level 0 (little debugging), level 1 debugs internal state changes, level 2 debugs events, and level 3 debugs IO calls. -f Run in foreground, this is suitable for running from init. -x Console mode: normally all messages are sent to syslogd (using local2 facility). With this option, all messages will be sent to std- out and cyclades-ser-cli runs in the foreground. This implies -f USE
Every instance of cyclades-ser-cli will have a virtual serial device which is a sym-link to a pseudo-tty. A terminal program can then talk to the virtual serial device and it's data transfers will be redirected across the network. Each virtual serial device will be accompanied by a Unix domain socket with the same name with the addition of ".control". So if cyclades-ser-cli provides the virtual device named "/dev/modem" then it will have a control socket named "/dev/modem.control". There is a shared object named libcyclades-ser-cli.so which intercepts calls to the tcsetattr() and tcsendbreak(). This shared object then sends the relevant data to the cyclades-ser-cli server via the control socket. To recognise a virtual modem device it has to read /etc/cyclades-devices. The libcyclades-ser-cli.so shared object can be loaded per-application through the LD_PRELOAD environment variable, or for the entire sys- tem through the system shared object configuration (see the OS documentation). Note that the LD_PRELOAD environment variable has to have the fully qualified path of the object, otherwise an application which changes it's current directory may fail. BUGS
In Solaris libcyclades-ser-cli.so does not work with the stty program. stty uses a different interface to this and requires some extra coding. In Solaris libcyclades-ser-cli.so conflicts with some system programs such as ps for unknown reasons. Just don't load it for those pro- grams, it has no such problems with any serial comms programs. EXAMPLES
Start an interface between /dev/prt1 device and a serial port number 10 of a Terminal Server named pr01, without hangup at last close: cyclades-ser-cli -c 1 /dev/prt1 pr01 10 In general use do not start cyclades-ser-cli from the command line, start it through the cyclades-serial-client script or from init. SEE ALSO
cyclades-serial-client(1), cyclades-devices(5) cyclades-ser-cli(8)
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