What is a TCP and UDP Port? How to block or open them in Windows 10?

If you are a network engineer or a normal user, you may need to find, open, or block a virtual port, such as a TCP or one UDP port for an application. Virtual ports help you manage the hardware and software on your network with respect to information traffic. In the language of a layman, virtual ports serve as dedicated channels for particular traffic such as website traffic, receiving emails, transferring files, and so on.

There are basically two types of virtual ports, namely TCP and UDP. TCP means Transmission Control Protocol; while UDP means User datagram protocol. TCP and UDP ports use different network protocols when managing information traffic. Network protocols are nothing more than a set of rules and regulations on how certain information should be sent and received. However, the base of a TCP or UDP port is IP, that is to say. Internet protocol.

Let's see how these two ports differ in their characteristics and functions.

How does a TPC port work?

A TCP port requires that users establish a connection between the sender machine and the receiver machine. It's pretty similar to making a phone call. Once the connection is established between the sender and the receiver, the information can be transmitted in both directions, until the connection is broken from the outside.

Although TCP is the most complex transport layer protocol, it is also the most reliable protocol when it comes to receiving error-free information. The protocol ensures that the destination machine acknowledges the datagram. This is only while it transmits the information. As a result, TCP is more commonly used than UDP.

How does a UDP port work?

A UDP port, on the other hand, does not require users to establish a connection between the sender and the receiver to send the information. However, unlike a TCP port, the information sent on the UDP port may not reach the receiver. It's like sending a letter. It is not necessary that the user has received the letter. Therefore, the information that needs to be broadcast is sent on a UDP port. The user set or listening to the specified UDP port can receive information.

UDP has a low latency and offers a constant flow of information. Thus, a UDP is the perfect choice for broadcasting broadcasts, online video games and voice over IP (VoIP) streaming. Therefore, a UDP port is only used when there is a specific need for the information sent.

Identify the right ports

There are many virtual ports available for any PC; that range from 0 to 65535. However, each of these ports has a certain standard and is dedicated to a certain application. Of these, some of the following ports use TCP and UDP.

• 20 (TCP): FTP (File Transfer Protocol)
• 22 (TCP): Secure Shell (SSH)
• 25 (TCP): SMTP (Simple Mail Transfer Protocol)
• 53 (TCP and UDP): Domain Name System (DNS)
• 80 (TCP): Hypertext Transfer Protocol (HTTP)
• 110 (TCP): Post Office Protocol (POP3)
• 143 (TCP): Protocol for Accessing Internet Mail (IMAP)
• 443 (TCP): Secure HTTP (HTTPS).

It is possible to check which ports on your Windows PC are open or closed. If you want to block or open a certain TCP or UDP port, here is the process.

Search for an open TCP or UDP port

Open the The Start menu. (For Windows 10, press the Windows button) and type CMD. Click now on Run as an administrator option.

When the prompt window opens, type Netstat -ab and press Enter. A list of TCP and UDP ports begins to appear with the IP address and other details.

The longer you wait, the longer the list of open ports becomes. Wait for the complete list to appear in the window. When the list is completely displayed, press CTRL + C and CTRL + V to copy and paste the information into Scratch pad or any other text editor.

As you can see in the picture above, the information in parentheses refers to the name of the program that uses an open TCP or UDP port. Next to the protocol name, you can see the IP address and the port number after the colon. For example, in 192.168.0.107: 50741, Numbers 192.168.0.107 are the IP adress, while the number 50741 is the port number.

Search for a blocked TCP or UDP port

To find out which ports are blocked by Windows Firewall, follow these steps.

The first step is the same as looking for an open TCP or UDP port. Open the Start menu by pressing the Windows button and type CMD. Click now on Run as an administrator option.

When the prompt window opens, type the following command: netsh firewall display status

Some ports may be blocked by the router or ISP and these may not be listed in the above list. To find these ports, type the following command: netstat -ano | findstr -i SYN_SENT

If this command returns no list, it means that none of the ports is blocked by the router or ISP.

How to open or block a TCP or UDP port

Now that you have identified TCP and UDP ports on your Windows PC, here is the most important part.

First, you may need to open a port for an application to work properly. On the other hand, you may need to block some ports because they are no longer used and can be a gateway for threats. As a result, these ports are blocked by the firewall.

Follow the steps below to open or block a TCP or UDP port.

Open the Start menu by pressing the Windows key. Type Windows Defender Firewalland select Windows Defender firewall with advanced security results.

The following window opens.

Click on Incoming rules in the left menu.

Click on New rule … in the Actions pane of the right menu. When this window opens, select Harbor radio button and click Next.

When in a hurry Next tab, the next window of New incoming rule wizard s & #39; opens. In this window, you can select the type of port you want to open or block. You can also choose to open or block all ports of the selected type or a specific local port. Specify the number or range of local ports that you want to open or block. And click Next.

The following window opens when you click Next. Here you can open the ports by selecting Allow connection or Allow the connection if it is secure radio buttons. Select the third radio button Block the connection to block the specified ports.

Select now if the rule applies to Field, Private or public or all that. Click on Next.

The following window opens when you click Next. In this window, specify a first name for this new incoming rule. You can also specify which ports have been blocked or opened in the The description section.

Click on finish to create this new incoming rule.

Please note that sometimes, after blocking a certain port, applications may not work properly. You may also experience problems connecting to certain resources. This means that the port you have blocked may need to be open. You can cancel port blocking at any time by following the same process.