Port Scanning
Port Scanning
Port-scanning is a process of probing a computer, server or
other network host for open ports. In networking, each application
running on a device is assigned an identifier called a port number. This
port number is used on both ends of the transmission so that the right
data is passed to the correct application. Port-scanning can be used
maliciously as a reconnaissance tool to identify the operating system
and services running on a computer or host, or it can be used harmlessly
by a network administrator to verify network security policies on the
network.
For the purposes of evaluating your own computer network’s firewall and port security, you can use a port-scanning tool like Nmap to find all the open ports on your network. Port-scanning can be seen as a precursor to a network attack and therefore should not be done on public servers on the Internet, or on a company network without permission.
To execute an Nmap port-scan of a computer on your local home network, download and launch a program such as Zenmap, provide the target IP address of the computer you would like to scan, choose a default scanning profile, and press scan. The Nmap scan will report any services that are running (e.g., web services, mail services, etc.) and port numbers. The scanning of a port generally results in one of three responses:
To run a port-scan for six common ports against your home router or firewall, go to the Nmap Online Port Scanner at https://hackertarget.com/nmap-online-port-scanner/ and enter your public IP address in the input box: IP address to scan… and press Quick Nmap Scan. If the response is open for any of the ports: 21, 22, 25, 80, 443, or 3389 then most likely, port forwarding has been enabled on your router or firewall, and you are running servers on your private network, as shown in the figure.
For the purposes of evaluating your own computer network’s firewall and port security, you can use a port-scanning tool like Nmap to find all the open ports on your network. Port-scanning can be seen as a precursor to a network attack and therefore should not be done on public servers on the Internet, or on a company network without permission.
To execute an Nmap port-scan of a computer on your local home network, download and launch a program such as Zenmap, provide the target IP address of the computer you would like to scan, choose a default scanning profile, and press scan. The Nmap scan will report any services that are running (e.g., web services, mail services, etc.) and port numbers. The scanning of a port generally results in one of three responses:
- Open or Accepted – The host replied indicating a service is listening on the port.
- Closed, Denied, or Not Listening – The host replied indicating that connections will be denied to the port.
- Filtered, Dropped, or Blocked – There was no reply from the host.
To run a port-scan for six common ports against your home router or firewall, go to the Nmap Online Port Scanner at https://hackertarget.com/nmap-online-port-scanner/ and enter your public IP address in the input box: IP address to scan… and press Quick Nmap Scan. If the response is open for any of the ports: 21, 22, 25, 80, 443, or 3389 then most likely, port forwarding has been enabled on your router or firewall, and you are running servers on your private network, as shown in the figure.
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