Port Checker

Discover and run diagnostic checks on your ports with the port checker tool.

Port checker

A port checker is a free, simple-to-use online checker tool that lets you find whether the ports in your computer are open or not. A port is an entity in the computer through which the exchange of information between multiple programs takes place. To understand the capability of the port for forwarding and receiving communications, the status of the port needs to be identified as open or closed. A port checker can also be used to check for vulnerabilities by finding if any open port is left unused.

Ports, along with IP address details, provide vital information about the system when it makes a request. Ports range from 0 to 65,536 out of which 0 to 1,023 are said to be well-known ports. These are some port numbers that are used for specific purposes.

What are well-known and registered ports?

Well-known ports are port numbers that are commonly used for everyday protocols, such as FTP, HTTPS, and IMAP, to name a few. The well-known port 25 is used for SMTP, 80 is used for HTTP, and so on. Registered ports are the port numbers of certain slots that are pre-booked by a client on a temporary basis. The pre-booking is usually done to conduct specific actions for their internal or personal use. Registered ports are also called ephemeral ports because they function for a short time.

Here are some of the commonly used ports numbers

The Internet Assigned Numbers Authority (IANA) reserved ports 0 to 1,023 for standard activities such as:

Port NumberProtocols

What happens when a port checker starts its scanning process?

A port checker sends a packet of data to a specific port that the user has looked up, and returns its status. One of the following three possibilities can happen:

  • The port could be open and ready to listen.
  • The port could be closed (i.e., currently in use) and not ready to listen.
  • The port could be silent, which indicates that it can be blocked, dropped, or filtered.

What are TCP and UDP ports?

TCP and UDP are the most commonly used protocols in computer networks for data transmission. A port checker follows either of the two protocols while transmitting packets through the network. Transmission Control Protocol (TCP) is more reliable because it provides a three-way handshake for establishing a secure connection between the sender and the receiver, and the packets are transmitted in order. User Datagram Packet (UDP), on the other hand, is faster and not as reliable as the TCP because they lag in error checking. These types of transmissions are often seen in live streaming and online gaming.

Port scanning techniques

There are multiple ways in which port scanning can be done. Some of the most common techniques are:

  1. Ping scan: A ping scan is the simplest technique of all. It sends a data packet as a ping request and checks the status of its port.
  2. SYN scan: A SYN, or half-open TCP scan, is a one-way handshake method. The checkers initiate a TCP connection and can identify if the port is open with the help of an ACK message. In this technique, the TCP connection is not fully established.
  3. TCP scan: A traditional three-way handshake takes place. It is as same as a SYN scan, but the full connection is established, unlike the half-open TCP scan.

What is a port scan attack?

Attackers can use this same port checker to inspect which port can be targeted because of a vulnerability. Usually ports that are open and unused for a long time can be a loophole for attackers to invade, as the open status helps attackers take control over the ports easily—even to destroy the application.

How a port check helps with security

Because a port scan attack happens mostly on an organization level, a business must ensure that it has a well-wrapped firewall, a private authorized access, and periodical checks on its unused network holes.

Frequently Asked Questions

  • What is the importance of port scanning?

    Scanning a port can get all sorts of vital information about the target system, and at the same time you will know which ports are currently open and which ones are at work.
  • How do I check if my ports are open?

    With the help of Zoho Toolkit's port checker, you can easily check whether a particular port in the system is open or closed. Simply enter the domain name and its port number and hit enter. The port checker will automatically update you with the status of that particular port.
  • Where do I check what port numbers are in use?

    With the help of the Terminal or Command prompt, you can easily find the port number that your system is using at moment. For windows, use netstat - a; for Mac, use netstat - an. This lists out all of your ports.

  • How do I close an unused open port?

    An unused open port can be closed in two different ways: You can permanently disable the service, or you can use a firewall to take proper measures. If you choose the first step, understand that the impact can be the port being permanently shut, and you won't be able to use it even after a reboot.