Why Use Telnet When You Have Netcat? A Swiss Army Knife for Sysadmins

From the day I started my career as a *nix admin, I always used to wonder why people don’t use multi-purpose tools or better alternates for existing ones. That is where Netcat (nc) kicked in—a zillion times better alternative to telnet with tons of functionality.

In today’s post, let’s explore why Netcat is considered the “Swiss Army Knife” of networking.

Basic Syntax

The basic syntax of the nc command is straightforward:

nc [options] [host] [port]

Netcat as a Port Scanner

One of the most common uses for Netcat is checking connectivity.

Testing TCP Connectivity Let’s check connectivity to port 80 of a webserver. We use -z (zero-I/O mode) to tell Netcat to report the status and then immediately close the connection. The -v flag provides verbosity so we can see the result.

nc -zv test.enigmabits.net 80
 Connection to test.enigmabits.net port 80 [tcp/http] succeeded!

We can do the same for port 22 (SSH):

nc -zv test.enigmabits.net 22
# Connection to test.enigmabits.net port 22 [tcp/ssh] succeeded!

Setting Timeouts In cases of high latency, we can use the -w option to set a timeout in seconds:

nc -zv -w 10 test.enigmabits.net 235
 nc: connect to test.enigmabits.net port 235 (tcp) failed: Connection refused

Checking UDP Ports

Netcat can also check UDP connectivity using the -u option:

nc -uz 8.8.8.8 53
# Connection to 8.8.8.8 port 53 [udp/domain] succeeded!

Scanning a Range of Ports You can scan multiple ports at once by providing a range:

nc -zv -w 1 test.enigmabits.net 21-30

Changing the Source Port If you need to originate your request from a specific local port, use the -p flag:

nc -zv -p 16000 test.enigmabits.net 22
Connection to test.enigmabits.net port 22 [tcp/ssh] succeeded!

Netcat as a Chat Medium

Who doesn’t want to have a quick chat with fellow sysadmins while sitting on the terminal of a remote machine? Netcat makes this incredibly simple.

• 1. On Machine A (The Listener):

nc -l 6666

• 1. On Machine B (The Connector):

nc machine_a_fqdn 6666

Now, whatever you type on one terminal appears on the other and vice-versa. It’s a perfect, lightweight way to communicate during a maintenance window.

Transferring Files

Netcat is surprisingly efficient for moving files without the overhead of SCP or FTP.

• 1. On the Receiving Machine: Prepare the machine to listen and redirect the output to a file:

nc -l 6666 > file_received
* 2. On the Sending Machine:
Pipe the file into the connection:

```bash
nc enigmabits.net 6666 < send_file
Once the transfer finishes, the connection closes, and your file is ready on the target machine.

Conclusion

We’ve only scratched the surface of what Netcat can do. While it works as a great alternative to telnet for simple port checks, its ability to listen, scan, and pipe data makes it much more powerful.

Enjoy feeding your NetCat today! 🐱