This post cover alternatives for checking open port without telnet. Some companies have strict policies and it can happen that telnet is not available.
And you know what? There is no requirement to install telnet. Just check the below alternatives.
Bash method
Bash is still the most popular shell. It is good to know this method because it is quite practical. It opens UDP or TCP connection to the corresponding socket.
- Successful connection
$ cat < /dev/tcp/localhost/22
SSH-2.0-OpenSSH_8.0
- Failed connection
$ cat < /dev/tcp/localhost/23
bash: connect: Connection refused
bash: /dev/tcp/localhost/23: Connection refused
Netcat method
Netcat is able to connect and listen on any port. It supports TCP/UDP ports.
- Successful connection
nc -zv -w 5 localhost 22
Ncat: Connected to localhost:22
- Failed connection
nc -zv -w 5 localhost 23
Ncat: Connection refused.
Curl method
Curl command is used to transfer data. It is great that it supports telnet protocol.
- Successful connection
curl telnet://localhost:22
SSH-2.0-OpenSSH_8.0
- Failed connection
curl telnet://localhost:23
curl: (7) Failed to connect to localhost port 23 after 0 ms: Connection refused
Python3 method
Python socket library provides direct access to the operating system socket interface.
- Successful connection
>>> import socket
>>> clientsocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
>>> clientsocket.connect(('localhost', 22))
>>> clientsocket.send(str.encode('\n'))
1
- Failed connection
>>> import socket
>>> clientsocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
>>> clientsocket.connect(('localhost', 23))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ConnectionRefusedError: [Errno 111] Connection refused
Perl method
Perl module named IO::Socket allows us to open the socket interface.
- Successful connection
use IO::Socket::INET;
$| = 1;
my $socket = new IO::Socket::INET(
PeerHost => 'localhost',
PeerPort => '22',
Proto => 'tcp',
);
die "$!\n" unless $socket;
print "Connected\n";
## PRESS CTRL+D !
Connected
- Failed connection
use IO::Socket::INET;
$| = 1;
my $socket = new IO::Socket::INET(
PeerHost => 'localhost',
PeerPort => '23',
Proto => 'tcp',
);
die "$!\n" unless $socket;
print "Connected\n";
## PRESS CTRL+D !
Connection refused
Thanks for reading. I'm entering the void. 🛸 ➡️ 🕳️