Test for network connectivity from various hosts to one specific host via ssh and telnet

Question

I am trying to see if a port is opened for a list of hostnames/IP's, and I used a simple script like this one to ssh to each host and capture the output.

for i in `cat $1`
do ssh $i "sleep 5 | telnet 11.22.33.44 123"
done

This is throwing a "No environment-specific terminal time" error because Telnet is designed to be an interactive tool to interact with a smart terminal.

How can I go around this, knowing that I cannot use nc command as it's not available on Unix AIX systems?

Please note that some hosts will reply with Connected to 11.22.33.44. Escape character is ^] and that means there is connectivity while others will freeze at Trying ... meaning that there is no connection.

Answer 1

Since perl is installed by default, one way would be to ssh to the intermediate host and ask it to run perl, with the perl program provided as a here-document:

for host in $(< "$1")
do

  ssh "$host" perl << 'EOF'
use IO::Socket;
my $handle = IO::Socket::INET->new(
        PeerAddr => '11.22.33.44',
        PeerPort => 123,
        Proto    => 'tcp',
        Timeout  => 5)
    or die "Failed\n";
close $handle;
print "Success\n";
EOF

done

The script attempts to connect to the given IP and port over TCP; if it fails, you'll get the Failed message, but if it succeeds, it immediately closes the connection and prints Success. This uses the $(< ...) syntax to read from the filename given by the first parameter; just like cat, this scheme assumes that none of the filenames have any characters from $IFS in them (spaces, tabs, or newlines by default). I've also quoted the loop variable (here, host), to prevent problems if any of the input file contents contain shell globbing characters like *, ?, or [.