Port scanners and open ports: What you should know

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Port scanners and open ports: What you should know

When it comes to securing your network from intrusion or attacks, one of the most commonly followed security measures is to regularly scan your network ports and close all open ports. This is because open ports can expose your network to several security vulnerabilities.

To tackle the risks introduced by open ports, network admins rely on port scanners. Port scanners help you identify, inspect, and analyze network ports, and aid in reducing your network’s attack surface by closing open ports. This makes port scanners an indispensable tool to ensure network security.

In this post, we discuss what open ports are, their vulnerabilities, and how you can defend your network with port scanners.

Network ports 101

Ports are the enablers of network communication. They help your network components and services exchange information by passing network packets. Between the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), there are 65,535 ports associated with an IP that are constantly being used by services and applications to send and receive message packets.

Among these 65,353 ports, ports numbered from 0 to 1023 are the well-known ports. These ports enable packet exchange between a host and a specific set of services. The services that can access these ports are established and are not subject to change. Some of the services using these ports include:

Port number

Associated port service


File Transfer Protocol


Simple Mail Transfer Protocol


HTTP for World Wide Web Services


SQL Services


Remote Desktop Protocol

Identifying port statuses with port scanners

Port scanners help you understand how your network ports are being used by triggering periodic scans. A port scanner determines the status of the ports using different network scanning protocols such as ping and TCP scans by sending a network packet to each port within the specified address range one at a time. Based on the scan response, port scanners assign the ports one of the following three statuses:

  • Open port: The port is configured to accept incoming network packets, meaning this port can establish a connection with a requesting network service.

  • Closed port: The port is configured to reject or ignore all incoming network packets. This indicates that the port is in use and cannot establish a connection.

  • Blocked port: The port did not respond to the port scan.

Open ports: What makes them a threat to network security?

Open ports can accept incoming network packets. Since they respond to port scans, an attacker can identify all the open ports in your network by simply conducting a quick scan. This means that open ports in your network can pose several security risk vectors including exposing your network vulnerabilities and becoming a passageway for intruders.

A port simply being open is enough for an attacker to establish a communication channel. It depends on whether a service is listening on a port and the nature of the service. Any open port that is left unmonitored might be running services that are unauthorized, misconfigured, or are easily exploitable. This makes the open port a valid target for attackers, because they open up your network to security issues such as:

  • Unauthorized network access: One of the top concerns with open ports is network intrusion by unauthorized entities such as malware and Trojans. They can run unauthorized services through open ports that might go unnoticed without periodic port scanning.

  • Exposed network weak spots: Attackers can establish communication with the services listening in your network's open ports, using which they can easily identify crucial network aspects such as the deployed use of the service, the software version, the underlying architecture, and communication models used. This can expose network vulnerabilities and poses a threat to your network confidentiality.

  • Interrupted network availability: By design, network ports cannot run more than one service at a time. This means that when one service is running on a port, no other service can use it. With unused network ports being open, attackers can easily launch denial-of-service attacks, which can render authorized applications unable to communicate with your network.

Port scanner: Your go-to network defense tool!

A straightforward approach to prevent attackers from exploiting your open ports is scanning and closing open ports before attackers access them. An effective way to do this is with the help of a port scanner tool. It will help you stay ahead of attackers and secure your network ports by conducting real-time port scans, determining port statuses, identifying port services, and using scan results to collaborate with other network tools.

Conducting real-time port scans 

You can trigger port scans across your network from your workstation. However, conventional processes and tools that require technical inputs such as CLI queries can make this task cumbersome and time-consuming.

Advanced port scanner tools like ManageEngine OpUtils simplify this task by triggering port scans after specifying the starting and ending IP addresses along with the port range to be scanned. Once triggered, the port scanner can run organization-wide port scans within minutes and displays various details about your ports such as the number of open ports, the services that are currently running, the response time, and so on.

Determining port status and identifying port services

Port statuses and the list of services running in ports are among the other details returned by a port scanner tool. You can use this list of services to cross-check with the list of authorized services and pinpoint unauthorized or malicious services running in your ports. Once pinpointed, advanced port scanning tools also help you close or block these ports from your central console. This enables you to secure your network against unauthorized network access, malicious services, and unexpected traffic flows into your network.

Using scan results to collaborate with other network tools

Independent port scanners are less effective when it comes to enhancing overall network security. Though they offer scan results that help you secure your network ports, it is also important to monitor other factors such as the IP and the status of the device associated with the port, the device's system snapshot, and more. This makes it important to choose a network tool set that comprises of an advanced port scanner along with other networking tools. This way, you can easily correlate data from network security tools like a port scanner and network scanner to ensure comprehensive network security monitoring and management.

If you are on the lookout for an enterprise-level port scanner that can scan, monitor, and manage your organization's ports and resources, try ManageEngine OpUtils! OpUtils is a comprehensive IP address management and switch port mapping solution. It offers advanced port scanning as a part of its network tool set that comprises of more 30 free networking tools. Why wait? Download a free, 30-day trial of OpUtils today!