Mar 22, 2018 Netcat is one of the most powerful and useful tool for testing and debugging the network and protocol connectivity.Though administrators use this tool for troubleshooting purposes, the attackers may use this for malicious intentions such as establishing a connectivity, transferring files, scanning ports etc.Netcat can act as in client-server mode as well. Netcat is a computer networking utility for reading from and writing to network connections using TCP or UDP. Objective: Learn netcat tool by doing the following activities: Use netcat to listen on TCP port 4000 of the localhost. Open a new tab and use netcat to connect to the listening instance. Use netcat to listen on UDP port 4000 of the. Netcat is not considered the best tool for this job, but it can be sufficient (a more advanced tool is nmap) nc -v -n -z -w 1 192.168.1.2 1-1000 The -n parameter here prevents DNS lookup, -z makes nc not receive any data from the server, and -w 1 makes the connection timeout after 1 second of inactivity.

The Netcat utility program supports a wide range of commands to manage networks and monitor the flow of traffic data between systems. Computer networks, including the world wide web, are built on the backbone of the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Think of it as a free and easy companion tool to use alongside Wireshark, which specializes in the analysis of network packets. The original version of Netcat was released back in 1995 and has received a number of iterative updates in the decades since.

Feb 10, 2020 Netcat is a command line tool responsible for reading and writing data in the network. To exchange data, Netcat uses the network protocols TCP/IP and UDP. The tool originally comes from the world of Unix but is now available for all platforms. Due to its universal usability, Netcat is often called the “Swiss army knife for TCP/IP”. Netcat for Windows. Netcat is a simple networking utility which reads and writes data across network connections using the TCP/IP protocol. It's a wonderful tool for debugging all kinds of network problems. It allows you to read and write data over a network socket just as simply as you can read data from stdin or write to stdout.

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'Netcat is the swiss army knife of networking utilities, learning to use it well has been incredibly helpful.'

Netcat Commands

What is Netcat Used For?

Netcat can be a useful tool for any IT team, though the growth of internally managed network services and cloud computing make that particular environment a natural fit. Network and system administrators need to be able to quickly identify how their network is performing and what type of activity is occurring.

Netcat functions as a back-end tool that allows for port scanning and port listening. In addition, you can actually transfer files directly through Netcat or use it as a backdoor into other networked systems. Partnered with a tool like Varonis Edge, you would receive an alert of any unusual activity and could then use Netcat to investigate. Lastly, Netcat is a flexible tool because of how it can be scripted for larger tasks.

Basic Netcat Commands

Once you have a Netcat application set up on your Windows or Linux server, you can start running basic commands to test its functionality. Here are a few to get started with:

nc -help – This command will print a list of all of the available commands you can use in Netcat. It will come in handy if you run into any errors while writing a script or are unsure of how to proceed.

nc -z -v site.com – This will run a basic port scan of the specified website or server. Netcat will return verbose results with lists of ports and statuses. Keep in mind that you can use an IP address in place of the site domain.

nc -l – This command will instruct the local system to begin listening for TCP connections and UDP activity on a specific port number.

nc site.com 1234 (less than) file_name – This command will initiate the transfer of a file based on the specified port number.

Printf – Netcat can actually operate as a simplified web host. This command will let you save HTML code and publish it through your local server.

Netcat Command Syntax

All Netcat commands must start with the “netcat” identifier or “nc” as a shorter option. By default, the Netcat tool will assume you want to perform a port scan unless you indicate otherwise.

Different option parameters can be used that include: “-u” for UDP traffic instead of TCP, “-v” for verbose output, “-p” to specify a specific port, and “-D” to turn on full debugging mode. Individual attributes within a Netcat command must be separated with a space. The command prompt will inform you if you have a typo or unrecognized term in your script.

Port Scanning with Netcat Commands

When trying to diagnose a network issue or performance problem, executing a port scan with Netcat is a smart first step to take. The scan will check the status of all ports on the given domain or IP address so that you can determine whether a firewall or other blocking mechanism is in place.

A basic port scan command for an IP ncat address looks like this:

nc -v -n 8.8.8.8 1-1000

Note that the numbers at the end of the command tell Netcat to only scan for ports between numbers 1 and 1000.

If you don’t know the IP address of a server or website, then you can look it up via a ping terminal command or just insert the domain into the Netcat command:

nc -v -n google.com 1-1000

You should always perform port scans when connected to your local enterprise network. If not, you can configure your router with a VPN service to create a secure tunnel into the network.

Create a Chat or Web Server

Chat programs are on the rise. From open-source solutions to those that seemed to suddenly gain massive popularity, there are a wide range of chat and communication tools available to enterprise organizations. The reality is that some IT experts and system administrators would prefer a simple text-only solution. Windows Netcat can actually fill that need and allow for the transmission of messages across a local network.

To get started, you first need Netcat to start listening on a port number. Make sure not to choose a port that is already in use by another application or service.

nc -l -p 1299

Then all you need to do is launch the chat session with a new TCP connection:

nc localhost 1299

This process can also be used to spin up a basic web server from your local machine. Netcat will function as the web host and allow you to store HTML content which can then be viewed through a web browser.

First, create a new text document on your local system and make sure to use valid HTML tags. Then save the file as “index.html” and store it in the root of your Netcat directory. Now switch back to the Netcat tool and run this command:

printf ‘HTTP/1.1 200 OKnn%s’ “$(cat index.html)” | netcat -l 8999

To see the HTML in action, simply open any web browser and navigate to your local IP address with: 8999 at the end to specify the port of the host.

Verbose Scan with Netcat Commands

Every command you run in Netcat will include certain output text to indicate whether it was successful or not. For troubleshooting and debugging purposes, you’ll want to gather as much information and logs as possible while also investing in solutions like Varonis Datalert to detect threats and respond quickly. Netcat can help thanks to the verbose parameter which can be added to any basic Netcat command. Simply include “-v” to your command and run it again.

Even with this setting turned on, Netcat will not reveal any of your credentials or authentication data.

HTTP Requests with Netcat Commands

We’ve covered how you can use Netcat to host HTML pages on your local system. But the utility program can also be used to make web requests to outside servers. In this way, Netcat will essentially function as a web browser by obtaining raw HTML code.

Along with a tool like Varonis Edge, Netcat can be helpful for IT professionals who are looking into internet traffic issues or proxies. Here’s an exam

Netcat Tool