How to Find Open and Blocked TCP/UDP Ports?

Find Open and Blocked TCP/UDP Ports:

There is a chance that the app that you are trying to run is complaining because the port is blocked or you have left a few ports open on your network which can lead to a security problem.

If you wish to know how to find open and blocked TCP or UDP ports, then read ahead. Before you move on and learn what ate TCP/UDP ports, you need to first learn what is a network port. 

What is a Network Port?

You must first know that the ports we are talking about are virtual. It has no connection with the physical network hardware ports on your computers, TV consoles, and routers. This is a way for network software and hardware to manage the traffic. Ports have a function that is a lot like reserved lanes on the road.

The sidewalk is for pedestrians. There is a different lane for buses and car vehicles. You can use one port for receiving emails and another for website traffic and file transfer requests. Ports are of two types i.e., TCP ports and UDP ports. 

What are TCP Ports and UDP Ports?

There are two common types of ports TCP and UDP ports. The first one is the transmission control portal and the other one is the User Datagram Protocol. Both ports use different network protocols. You can use these as a distinctive set of rules for how you can send information and then receive it.

They both are built on basic internet protocol, which makes the home network and internet work. Nevertheless, they are good for many different applications. 

Whenever you try to send this information over UDP, then sender is not required to establish a connection with the receiver before you begin the conversation. This is somewhat similar to sending a letter. You don't know whether the other person has received your message or not and there is no guarantee of a response from the other side.  

TCP is a lot like making a phone call. The receiver is required to pick up a connection and there's a flow of information going back and forth until someone hangs up intentionally. UDP messages are literally broadcast over the network for anyone who is listening to a particular UDP port. This is perfect for housekeeping-type messages that relate to streaming broadcasts and online video games. 

Which Ports are Open by Default? 

There are various ports. A port number may range anything from 0 to 65535. It doesn't mean any app can pick up any port. There are some ranges and established standards that will help you make sense of the noise.

Port number 0 to port number 1023 are the necessary ones and involve basic network services. It makes sense as the lower-numbered ports were assigned earlier. The SMTP protocol for email is particularly used by port number 25. 

Port number 1024 to port number 49151 are registered ports and are given or assigned to common services like Open VPN on port 1194 or SQL on ports 1433 and 1434. Other port numbers are private and dynamic.

These port numbers are not reserved and you can use them on any network you like to support a specific service. This problem appears when two or more services are on the same network using the same port. It is not possible to list every port that is important.

However, there are some ports that are very common and easy to remember. 

• 20 - File transfer protocol
• 22 - Secure Shell
• 25 - Simple mail transfer protocol
• 53- Domain name system
• 80 - Hypertext transfer protocol
• 110 - Post office protocol
• 143 - Internet message access protocol
• 443 - HTTP secure

As there are a lot of common port numbers, the best way to remember them is to remember the ranges. This will tell you whether a port s reserved or not. Thanks to Google, you can search for the services that use a particular port. 

Search for Open Ports in Windows

After getting to know the basic information about TCP and UDP ports, you need to know which ports are open and which you can use on your computer. The great thing is that Windows has a very helpful command that will show you the ports that are currently in use on your PC by different apps and services. 

Step 1: First of all, you are required to go to the Start menu and then look for CMD. 

Step 2: After that, go to CMD and then right-click on it. After that, select the option of Run as administrator. 

Step 3: On your command prompt, type Netstat -ab. 

Step 4: Now, a long scrolling list will appear on the screen before you. All you have to do is to copy and paste this information into a text editor. 

Step 5: The details you see in the brackets are actually the name of the program that is using the port. The number has an IP address and port number after a colon. 

Scan for Blocked Ports

Now you need to find out the ports that are being used and by which app. However, it does not tell the ports that are actively blocked by the Windows firewall deprecated, 

• Go to the Start menu and then start looking for CMD. 
• After that, navigate to CMD and then right-click on it. 
• Launch the command prompt and then type "netsh firewall show state". 

This is actually a display of blocked and open ports according to the configuration of your Windows firewall. You will see that the command is being. However, the new command is not going to display the information you wish to watch.