Open Port Checker Guide

Open port checker refers to the method of port scanning using a tool to identify unnecessary ports that are open. Once we have that list we can close them. In real life we will try to understand why this port was open, what is the service that use this port and information related to the data that was send using this port. This part will be execute before closing the port. By taking down the service that open the port.

Open Port Checker
Open Port Checker

A Complete Guide on Open Port Checker

In today’s world, internet is the most used service. A life without internet connection and Wi-Fi system is unimaginable. The wide use of internet across the globe has resulted in the invention of open port checker.

These port scanners are tools that scan and IP address or a network looks for open ports in them. A web-based port checker tool helps to scan the environment from outside its LAN (local area network).

It is common to have ports that are open. For example, a web server, like IIS, Internet Information Service, or Apache will open ports for incoming connection. Its default fort will be 80 for HTTP protocol and 443 for HTTPS protocol.

Uses of the web-based port checker:

As mention above. Online open port checker (or web-base) is useful to find if a particular port is configured properly. If it needs to allow connection it need to be open. Like our IIS/Apache.

It can also be used to scan for ports that know to be use by malware or just to check if there are unknow open port in the environment. After all an open port is an entrance to the inner environment.  

Online open port checker (or web-base) is useful in finding out if a particular port forwarding set up is configured properly.

It can help to check if service is blocked by firewall or not. Further to this, the tool can be used to check the network for port forwarding configuration.

For instance, some ports like port 25 is mostly kept blocked in order to protect the system from malicious activities. This blocking is done at the ISP level itself. The checker often helps to diagnose the problem.

Free online port checker:

Online port checkers are simple to use and are mostly found free on the internet. Most of them receive an input IP number or domain name and port or list of ports.

Once they start the checking process it will send a package to the port trying to connect to it. If success the remote port is open. If not, the remote port is closed.

Using port checkers on a regular basis is good from security perspective. You do not want to find open ports in your environment that you are unaware of. It might indicate that you had been hacked and someone is connected to your system.

Open port and security:

Network ports act as the entrance to a system that connected to the internet. Usually, through internet a lot of data is sent and received from the client application.

This too and from transmission of data and information is a normal behavior of the system. Hackers and penetration testers will over abuse the system to revile vulnerabilities.

If vulnerabilities are founds it can be used to create an exploit. An exploit can be use to hack into the system and to gain access or control to the local file system and sensitive data.

This can lead to an urgency where it is necessary to get the ports checked, monitored and closed. From security perspective this ensures more verification against malwares and hacker.

Offline port checker:

Now we will talk about offline port checker. Every device that connect the internet or intranet (local network) use a port.

There are some free tools that one can run on his system to find out what ports are currently open. An easy example is netstat command line tool. More on netstat can be found on our netstat page.

It is not really offline, after all we do need connectivity, here offline is referring to the LAN. If you are a home user. Your computer and mobile device connect to the internet using a router (or modem).

Router, local IP address:

The router gives you an inner address that you can use. Once you try to enter a website it will pass your request within the router to the remote web server.

So, your computer has a local IP address (start with 10 or 192 on IP v4) and once you enter the internet you are using another IP address.

With the right knowledge you can connect your mobile device to your computer using your local network. If you check your computer or mobile device for its IP address you will notice that they are almost the same. Assuming your mobile device is  connected to your WiFi network.

External port checker does not have direct access to your computer they also have to pass through the router.

Port scanners extra info:

Offline port scanners tool can use some connection method. In TCP you can do a full connection aka connect(). this process is done on 3 steps. Also known as 3 handshakes.

The tool can send a package that include only the first part of the handshakes. If it mange to get a respond back it close the connection without send the last part. It knows that the port is open. Due to the fact that it gets a respond.

Advanced scan tool can use IP packets to figure out what is the target operating system and what it the service that open the port. This can done using signature base mechanism.

When is port checking done?

Online port checking can be use mostly during one of the following:

  • The initial stage of a penetration test. Done at an early stage to find out all the network entrances into the system. Port scanning performs differently for TCP and UDP ports.
  • When configuring port forwarding on the router.
  • To check if unnecessary ports are open.
  • From security perspective.
  • To check if port is open or not.
  • A web-based port checker is useful to inhibit malicious activities on an internet network. It is advise to choose the best online tool to complete the check.
  • Service uptime.

Offline port scanning can be use for:

  • To find unnecessary ports.
  • Check for known malware port in use.
  • Check the firewall configuration.
  • More.

Please note: Behind open port there is a service (like an exe file) that running and waiting for connections. A software that is representing a server service. You might fine a running service that is unfamiliar. The admin can close it in the firewall or router and stop the running service.

In conclusion:

Online open port checker can be easy to use. To check a port, you required to enter the host-name or the IP address of the target and the port in the provided field.

Some will ask you to provide a port. Some will have a list of default port that they scan.

The greater the difference between the start port and the end port, the longer it will take to finish the scan.

Open port checker can bring you good to know info on open port, port forward configuration, service status  and a service uptime.



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