Re: Telnet over SSH2 from Windows

[salva]

If tunnels are not forbidden in the intermediate host, you could use some SSH client (OpenSSH or plink from PuTTY) to create a tunnel from your local machine to the target device telnet port. Then, use Net::Telnet to talk to the remote machine through the tunnel.

If tunnels are not enabled, you could run netcat or socat in the intermediate machine to obtain a similar effect. I believe that later versions of Perl for Windows already have an emulation of socketpair, so you would be able to do something like...

     
Net::Telnet ===> socketpair ===> plink  ===> netcat ===> destination h
+ost/port
   \_______________  ____________/   \___  ___/
                   \/                    \/
               Local machine     Intermediate machine

[Hessu]

Hello,

Plink was nice suggestion because it worked. With command string below, I was able first to establish tunnel via SSH server to the device with telnet and command it with Net::Telnet. The plink command explanation can be found from plink documentation and it is also quite nicely explained in HOWTO ssh port-forwarding.

I am still more than happy to hear explanations why reading during telnet session seems to break the write and if this is somehow doable from Windows.

Thank You

# From DOS prompt, give command below and leave the session open.
# Version 0.60 from plink is needed because it contains the -nc
# parameter. Version 0.58 did not have this parameter. The remote
# host in here is the device IP address being access via telnet.
#
# plink.exe -L 1555:(remote host):(remote port) (ssh server) -l <user 
+name> -pw <password> -nc (remote host):(remote port)

#!/usr/bin/perl -w

use strict;
use warnings;

use Net::Telnet;
use Data::Dumper;

my $telnet   = ();
my @l_resp_a = ();

$telnet = Net::Telnet->new( Timeout => 10,
                            Host    => 'localhost', # or 127.0.0.1
                            Port    => 1555 );

if( $telnet ){
  print "connected\n";
  $telnet->prompt('/<expected prompt>/');
  $telnet->cmd( String  => 'ls -al',
                Output  => \@l_resp_a );
}
else{
  print "failed to connect";
}