Nmap stands out among other monitoring and vulnerability scanning solutions used by cybersecurity professionals because it is free, incredibly flexible, portable, well-documented, and simple to use.

Various abilities are combined into one package with Nmap, which makes those familiar with command-line interfaces much more comfortable. This article will discuss how to use it for port scans, other useful Nmap functions, and why threat actors also use port scanning.

What is a Port Scan? How Do You Run It? 

Port scans are a type of vulnerability scanning used to identify open ports on a server that send or receive data. Open ports can lead to data and network security issues, making your company more susceptible to cloud security breaches. To run a port scan, you enter the domain or IP address into the port scanner tool, which then examines the entire network for any cybersecurity vulnerabilities related to open ports. Network mapping with port scans is an effective way to find network security threats within a system. As a result, they can help you to close ports and protect your business. 

What are Ports and Port Numbers?

A port is the starting and finishing point of online communications. Ports are typically linked to a specific function or operation, are software-based, and are managed by the company using the service. Port numbers are identification codes that help a server manager determine where a network packet should be sent. This allows a steady stream of communication between two parties. However, open ports without the proper configuration are an invitation for network intrusion and a whole host of preventable security threats.

How Do You Scan Ports on Nmap?

The simplest way to start port scanning is to enter nmap , where is the name of a network host. From this command, Nmap converts the hostname to an IP address, pings the host, and then returns a list of port statuses for the most popular 1,000 ports listed in nmap-services. This report categorizes all ports as open, closed, filtered, unfiltered, open|filtered, or closed|filtered. Similar results are condensed into a single line, while notable statuses are highlighted for the administrator to read. 

Can You Detect an Nmap Scan? 

Nmap scans run by cybercriminals are not always picked up quickly, if at all. Threat actors can use Nmap to find vulnerable server hosts that they will target for an attack. Modern forms of port scanning detection can pick up on Nmap scans, but the best defense against hostile scanners is to stay a step ahead by preemptively scanning your ports. It is important to be aware of any and all cybersecurity vulnerabilities within your company. Routine network mapping scans will notify you of open ports so you can close them before a breach. Within Nmap, there are options listed that you can select to verify your system has proper data and network security with scanners.

How to Scan with Nmap

Here are a few of the more popular scans customers use with Nmap:

Ping Scans

The most basic function of Nmap is to identify hosts on your network, which can be done through a ping scan. This scan logs all IP addresses and hosts without sending packets to the admins. You can run more commands on the found hosts to examine them more thoroughly. Run the following command to execute a ping scan:

# nmap -sp 192.168.0.1/22

Host Scans

Host scans are a powerful technique that can be used to verify data and network security. They send ARP request packets to all the hosts on your network, who respond with the ARP packet status and MAC address. Run the following command to execute a host scan:

# nmap -sp

OS and Services Scans

Nmap can run scans to detect the operating system, version, and services on a single or numerous devices. Detection scans are important to the enumeration process when conducting network penetration testing. It's critical to know where susceptible devices are on the network so they can be repaired or replaced before any attacks on network security can get to them. Run the following command to detect OS and Services:

# nmap -A

How Can You Prevent Port Scanning?

You can prevent a port scan by installing a super-strong firewall. This keeps external networks from looking at your business’s protection (or lack thereof). If a firewall sees that someone is trying to execute a port scan, the firewall will shut the port scan down.

How Do Bad Actors Use Port Scanning as an Attack Method? 

Cybercriminals will use port scanning to identify cybersecurity vulnerabilities in your company’s system. Network mapping helps them to find the easiest ways to access your sensitive information and collect your data. Threat actors will scan the company, identify where they can break into your business assets, and execute cloud security breaches.

Final Thoughts on Port Scanning with Nmap 

Nmap can be used to perform various scans to gather information for network discovery and auditing. Vulnerability scanning provides actionable intelligence and ensures that your company's data and network security is not an unknown variable. This way, administrators can detect weaknesses before they become a problem. Using Nmap or other network mapping tools for firewall pentesting is an important step towards improving your overall security posture.