Analysing Port Scanning In Network Security
Port-scanning in network security is a process of probing a computer, server or other network hosts 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 a 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 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 execute a port-scan of your network from outside of the network, you will need to initiate the scan from outside of the network. This will involve running a Nmap port-scan against your firewall or router’s public IP address. To discover your public IP address, use a search engine such as Google with the query “what is my ip address”. The search engine will return your public IP address.
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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