Network scanning is the process of identifying active devices connected to a network. It relies on specific functions built into network protocols to send requests to devices and wait for their responses. In most cases, network scanning is used to monitor and manage network environments. However, it can also help proactively detect vulnerabilities that cyberattackers might exploit.
A wide range of network scanning tools is available, from open source utilities to commercial scanning platforms. Each platform provides a different set of capabilities. Selecting an appropriate tool therefore depends on whether its features match the requirements of the organization.
How does network scanning work?
The exact protocol mechanisms used during a scan depend on the type of network being examined. In Internet Protocol (IP) networks, scanning typically involves sending a simple request, such as a ping, to every possible IP address within a defined range. When an address responds to the ping, the scanner can use additional protocols to collect more information about the corresponding device. This approach is known as active scanning.
Passive network scanning works differently. Instead of sending requests to systems, it continuously monitors network traffic for possible risks. These can include malicious code or other suspicious activity. Potential issues are then flagged for further investigation.
Within network monitoring and management environments, administrators commonly use scanning for three core management purposes:
- To apply network discovery capabilities to identify network users and create an inventory of them.
- To determine the current condition and status of systems and devices.
- To build an additional inventory of network components and compare it with the list of devices expected to be present. This comparison can be used as an indicator of overall network health.
Cybercriminals can use the same scanning protocols and tools employed by network administrators to investigate potential targets. In a malicious scenario, an attacker may first determine the IP address range assigned to an organization through the domain name system or the WHOIS protocol. The addresses within that range can then be scanned to identify servers, operating systems, system architectures and available services. After that, the attacker may attempt to reach open ports that are not properly secured in order to compromise target systems or applications.
Why is network scanning important?
The large number of cyberthreats that emerge every day, combined with the breadth of potential network vulnerabilities, makes scanning an important part of maintaining network health and reducing exposure to cyberattacks. Network scanning is a fundamental network security capability and should be performed regularly. Threats can emerge very quickly, so scanning plays an important role in detecting and troubleshooting potential vulnerabilities and security risks.
Frequent scanning is essential for obtaining effective results, even though the scanning process can cause a slight temporary reduction in network performance. Network scanning tools can produce a detailed view of the environment and provide information such as:
- An inventory of all devices connected to the network.
- Information about important access points, including ports.
- Detection of suspicious packets moving through the network.
- Network performance information presented through dashboards.
- Reports describing the current state of the network.
Overall, network scanning helps cybersecurity and network security administrators identify potential weaknesses before hackers and other threat actors can take advantage of them.
Network scanning steps
Most network scanning processes include the following four steps:
- Inventory. The scanning tool first examines the network to build an inventory of all connected devices.
- Network map. If the scanning platform includes this capability, it can generate a map of the network topology. Nmap, short for Network Mapper, is a command-line port scanning tool that can be used to identify systems present on a network and map connected devices. This open source utility can scan large and diverse network environments. It can identify active and inactive hosts or ports and assess network perimeter components, including firewalls, intrusion detection systems, intrusion prevention systems and other network parameters.
- Health and vulnerability check. The next stage can involve the Address Resolution Protocol, which examines network addressing at the primary network and subnet levels for suspicious activity. The Internet Control Message Protocol can be used for broader scans, including scans of systems located in other geographic regions. More advanced protocols can also be used to collect detailed information about network health and identify potential vulnerabilities.
- Reporting. Information collected by scanning tools is often displayed on dashboards in real time. Specific parameters can be highlighted, and recommendations for mitigating attacks may also be provided. Scanning platforms can additionally generate documented reports for auditing.
What types of network scans are available?
Network scans generally fall into two primary categories: active scanning and passive scanning. They can also be divided into several more specialized types:
- Host scanning. Host systems are important targets for hackers, which makes it necessary to scan hosts and determine their current status. One approach is to send a ping to every IP address. The request prompts a host to return a response containing information about its status. Hosts that fail to respond can be placed on a list of potentially vulnerable targets. Hackers also commonly use host scanning to identify systems that might be suitable for exploitation.
- Port scanning. A port scanner identifies ports that may be malfunctioning or potentially compromised. The scanner sends packets to different ports and analyzes the responses generated while attempting to connect to services running on those ports. Hackers also use port scanning to identify potential targets.
- Network scanning. This type of scan examines IP addresses and identifies operating systems and devices connected to the network. It can also be used to create a network map.
- External vulnerability scans. These scans search for weaknesses and security flaws within the network. Examples include outdated or improperly configured firewalls and security systems, exposed ports, insufficiently patched devices and insecure Internet of Things endpoints. Vulnerability scanners assess network infrastructure and connected devices from the perspective of a potential attacker.
- Total assessment scan. This type of scan evaluates devices associated with every IP address and checks them against multiple conditions. These can include the device’s overall security status, patch status, most recent usage, presence of antivirus software and presence of endpoint detection and response systems.
- Penetration testing. Also known as ethical hacking, penetration testing or pen testing attempts to simulate a real attack. It can involve bypassing existing perimeter security controls, searching the network for vulnerabilities, identifying exploitable systems and data, and conducting a detailed assessment of network risk. Appropriate authorization from users and clients should be obtained before a penetration test is performed.
Network scanning best practices
Several practices can help improve the effectiveness of network scanning:
- Regularly inspect both internal and external devices across the network infrastructure.
- Establish a documentation process that supports troubleshooting, security assessments, planning, status reporting and the creation of audit evidence.
- Prioritize scanning activities according to the business criticality of each device.
- Define a consistent schedule for frequent network scans.
- Automate scanning at predefined times or in response to specific conditions when the selected scanning tool supports automation.
- Regularly review and adjust scanning parameters to reduce both false positives and false negatives.
