Open Port Checker

Open Port Checker is an online service which lets you check if a port is open or not on a host and test port forwarding on your router. This tool is free-of-charge, easy-to-use, secure, and accessible from any device. You can do unlimited online tests, no need for installations. This Open Port Checker tool supports the check by hostname, IPv4 and IPv6 addresses.

FTP(21), SSH(22), Telnet(23), SMTP(25), DNS(53), HTTP(80), HTTPS(443), POP3(110), IMAP(143)

A port is a communication endpoint on a computer or a network device, such as a router. It is used to identify a specific process or service and allow it to communicate with other devices on a network. Ports are identified by a unique number, called the port number. When a device connects to another device on a network, it does so by specifying the IP address of the target device and the port number of the service or process it wants to communicate with. This allows the target device to identify the specific service or process that the connection request is intended for, and to route the traffic accordingly. For example, HTTP traffic is typically sent to port 80 on a web server, while HTTPS traffic is sent to port 443.
Ports are divided into three ranges:

• Well-known ports (0-1023): These ports are reserved for use by system-level or privileged services and typically require superuser privileges to bind to.
• Registered ports (1024-49151): These ports are intended for use by specific services and are registered with the Internet Assigned Numbers Authority (IANA).
• Dynamic/private ports (49152-65535): These ports are intended for use by client applications and are typically used for outgoing connections.

Each Internet Protocol (IP) address can have 65,535 ports available. A port number of zero is used to assign a random port number. A port can be thought of as a virtual door on a computer.

An open port is a network port on a host that is configured to accept incoming network traffic. This means that the host is listening for incoming connections on that port and will respond to any traffic that is sent to it. An open port can be used to access a specific service or application running on the host, such as a web server, email server, or remote access service.
Open ports are a potential security risk as they can be targeted by malicious actors attempting to gain unauthorized access to the host. It is important to regularly check for and close any unnecessary open ports on a network to minimize security risks.

A closed port is a network port that is not currently in use or available for communication. In the context of a TCP/IP network, a closed port is one that is not open, meaning that there is no application or service currently listening on that port and accepting incoming connections. In other words, it is not accepting any incoming traffic to that port.
When a device, such as a computer or server, receives an incoming connection request to a closed port, it will respond with a "connection refused" message. This is because there is no application or service on the device that is configured to listen on that port and accept incoming connections.
Closed ports can be used as a security measure, as it can help to prevent unauthorized access to a device or network.

Port forwarding is a network technique that directs incoming network traffic on a particular port to a specific internal IP address and port. It is used to allow remote hosts to connect to a specific device on a private network behind a router or firewall. In a typical home network, a router is used to connect multiple devices to the internet. The router assigns a unique private IP address to each device connected to it. These private IP addresses are not accessible from the internet. When a device on the internet, such as a remote computer, wants to connect to a device on a private network, it sends a request to the router's public IP address. The router then uses port forwarding to determine which internal device should receive the incoming connection request. For example, if you have a web server running on a device with the private IP address of 192.168.1.100 and you want to allow incoming connections to it from the internet, you would set up port forwarding on the router to forward incoming traffic on port 80 (the default port for HTTP traffic) to the IP address of the web server, 192.168.1.100. This way, when someone attempts to connect to the router's public IP address on port 80, the router will forward the request to the web server, and the web server will respond. Port forwarding can also be used to access services like Remote Desktop, SSH, FTP, and others that are running on a device behind a router. It is important to note that port forwarding can also be a security risk. If not configured correctly, it can allow unauthorized access to a device or network. It is also important to use a firewall that blocks all incoming traffic except traffic to the forwarded ports, to prevent unauthorized access.

Opening a port and forwarding a port are related but distinct concepts.

Opening a port refers to configuring a host or device to allow incoming connections on a specific port. This is done by configuring the host or device's firewall to permit incoming traffic on that port. Opening a port is necessary for the host or device to be able to receive incoming connections on that port.

Port forwarding, on the other hand, is a technique used to redirect incoming connections on one IP address and port number to a different IP address and port number. This is typically done using a router, which acts as the gateway between the private network and the Internet. The router is configured to redirect incoming traffic on a specific port to a specific device or service on the internal network. The goal of port forwarding is to allow external traffic to reach a specific device or service on a private network, such as a home network.

So, to put it simply, opening a port is the first step to allow traffic to reach the device and forwarding a port is the second step to direct the traffic to a specific service or application running on the device.

An open port check can be used for several purposes, including:

• Network troubleshooting: An open port check can be used to identify which ports are open and listening on a specific device. This can help to identify and diagnose network connectivity issues, such as a firewall blocking a necessary port or a service that is not running or configured correctly.
• Security assessment: An open port check can be used to identify which ports are open and listening on a device, and it can also be used to identify potential vulnerabilities in a network or device. For example, if a port that should be closed is found to be open, it may indicate that a service or application is not configured correctly, which could leave the device or network open to attack.
• Remote access: An open port check can be used to identify which ports are open and listening on a device, which can be useful for remote access to a device or network. For example, if you want to remotely access a device using SSH, you would need to ensure that port 22 is open and listening on the device.
• Service discovery: An open port check can also be used to discover which services are running on a device or network, and which ports they are using. This can be useful for identifying potential vulnerabilities, or for determining which ports to block or allow through a firewall.
• Compliance: Some industries or organizations are required to follow specific compliance standards, such as PCI-DSS or HIPAA. These standards often require regular port scanning and vulnerability assessments to ensure that the network and devices are secure. An open port check is an important step in this process.

It's important to keep in mind that an open port does not always mean the device is vulnerable, as it depends on the service or application listening on that port, the type of traffic it handles and the configuration of the device and the service.

Open Port Checker can test a router's port forwarding setup by sending a request to the router's public IP address on the specified port, and checking for a response. If the port is properly forwarded, the request will be forwarded to the internal IP address and port specified in the router's port forwarding configuration, and the online checker will receive a response.

If the router's port forwarding configuration is set up correctly, Open Port Checker should be able to connect to the internal IP address and port. If the connection is successful, the port is considered open and the port forwarding is working.

However, it's worth noting that Open Port Checker can only check if the port is open from their server location and doesn't guarantee that the port is open and accessible from any other location or network. Also, there are some firewalls, security settings and ISP level restrictions that can block the connection even if the port forwarding is set up properly.

Open port does not immediately mean a security issue. But, it can provide a pathway for attackers to the application listening on that port. Malicious hackers commonly use port scanning software to find which ports are "open" in a given computer, and whether or not an actual service is listening on that port. They can then attempt to exploit potential vulnerabilities in any services they find.

Pinging a port refers to using the "ping" command to check the status of a network connection on a specific port. The "ping" command sends an Internet Control Message Protocol (ICMP) echo request packet to a specified IP address, and waits for a response.

When you "ping a port" you are trying to establish a connection to a specific port on a device using the same ICMP echo request packet, but this time the goal is to verify if the port is open and reachable. This is done by sending a packet to the target machine on the specified port.

It's important to note that some firewalls and security configurations are set to ignore ping requests, so you may not always be able to ping a port even if it is open. Additionally, some devices or services may not respond to ping requests on specific ports.

Using a tool like nmap or telnet is a more reliable way of testing for open ports.

• Open the Open Port Checker Tool
• Enter a domain or an IP address in the space provided (Both IPv4 and IPv6 addresses are supported)
• Click on the "Check Port" button

The Open Port Checker Tool will then test and scan open ports on your connection and gives you the test result.

Having the server domain: telnet [DOMAIN] [PORT_NUMBER] (Ex: telnet domain.com 80)
Having the server IPv4 Address: telnet [IPv4Address] [PORT_NUMBER]
Having the server IPv6 Address: telnet [IPv6Address] [PORT_NUMBER]

1. Activate Microsoft Telnet Client (Control Panel/Programs and Features/Turn Windows features on or off)
2. Open the command prompt and run telnet to to open the Microsoft Telnet Client
3. Run the following commands for testing a server open ports:
Having the server domain: telnet [DOMAIN] [PORT_NUMBER] (Ex: telnet domain.com 80)
Having the server IPv4 Address: telnet [IPv4Address] [PORT_NUMBER]
Having the server IPv6 Address: telnet [IPv6Address] [PORT_NUMBER]

Port number	Protocol/Service
20 & 21	FTP (File Transfer Protocol)
22	SSH (Secure Shell)
23	Telnet, a Remote Login Service
25	SMTP (Simple Mail Transfer Protocol)
53	DNS (Domain Name System)
80	HTTP (Hypertext Transfer Protocol)
110	POP3 (Post Office Protocol 3)
115	SFTP (Secure File Transfer Protocol)
123	NTP (Network Time Protocol)
143	IMAP (Internet Message Access Protocol)
161	SNMP (Simple Network Management Protocol
194	IRC (Internet Relay Chat)
443	SSL / HTTPS (Hypertext Transfer Protocol Secure)
445	SMB
465	SMTPS (Simple Mail Transfer Protocol over SSL)
554	RTSP (Real Time Stream Control Protocol)
873	RSYNC (RSYNC File Transfe Services)
993	IMAPS (Internet Message Access Protocol over SSL)
995	POP3S (Post Office Protocol 3 over SSL)
3389	RDP (Remote Desktop Protocol)
5631	PC Anywhere
3306	MySQL
5432	PostgreSQL
5900	VNC
6379	Redis
11211	Memcached
25565	Minecraft

A Port Tester is another name used to mean an Open Port Checker

A port scanner is a software tool or utility that is used to scan a network host for open ports. It works by connecting to a specific host and then attempting to connect to various ports on that host to see if they are open or closed. An open port is one that is listening for incoming connections, while a closed port is one that is not listening. Port scanners can be used for a variety of purposes, including network troubleshooting, security testing, and network mapping. For example, a network administrator might use a port scanner to identify open ports on a host and then close them if they are not needed. This can help to improve security by reducing the number of potential attack vectors. There are many different types of port scanners available, including both command-line and GUI-based tools. Some popular examples include Nmap, Zenmap, and Angry IP Scanner.

There are different types of port scanners, such as:

• TCP connect scanner: This type of scanner establishes a full TCP connection to each port it scans, and then closes the connection. It is the most basic and simplest form of port scanning.

• SYN scanner: Also known as a stealth scanner, this type of scanner sends a SYN packet to each port it scans, and waits for a SYN-ACK or a RST packet. This type of scanner is more stealthy than a TCP connect scanner, as it does not establish a full connection.

• UDP scanner: This type of scanner sends a UDP packet to each port it scans, and waits for a response.

• ACK scanner: This type of scanner sends an ACK packet to each port it scans, and waits for a RST packet. It is used to map out firewall rule sets.

• FIN scanner: This type of scanner sends a FIN packet to each port it scans, and waits for a RST packet. It is similar to an ACK scanner and is used to map out firewall rule sets.

• Xmas scanner: This type of scanner sends a packet with the FIN, PSH, and URG flags set, to each port it scans, and waits for a RST packet. It is similar to an ACK and FIN scanner and is used to map out firewall rule sets.

Port scanners can be used for both legal and illegal purposes, such as by system administrators to identify and fix vulnerabilities in their networks, or by attackers to find potential targets for exploitation.

It's important to note that port scanning can be illegal and considered as a hacking attempt if it is done without proper authorization. So, it is always a good practice to take permission before doing any scan.