Linux Tactic

Understanding Ports: Categories Functions and How to List Open Ports on Linux

Ports are an essential part of networking, and they play a significant role in facilitating communication between devices. In this article, we’ll be discussing what ports are, the function of ports, their categories, and how to list open ports on Linux.

Understanding Ports: Definition and Function

Before we dive in, let’s start with the basics. What are ports, and what do they do?

A port, in networking terms, is a 16-bit number that is used as an endpoint for communication. Ports provide a way for traffic to be directed to the correct process or service on a device.

When a device wants to send data to another device, it needs to know the destination IP address and port number. The IP address defines the destination device, while the port number tells the device what process or service to send the data to on that device.

Ports are specific to a particular protocol, such as TCP or UDP.

Categories of Ports

Now that we’ve covered what ports are and their function let’s discuss the different categories of ports.

Well-Known Ports:

The Internet Assigned Numbers Authority (IANA) defines the

Well-Known Ports as port numbers ranging from 0 to 1023. These ports are standardized and reserved for specific services.

Some examples of well-known ports include port 80, used for HTTP traffic, and port 443, used for HTTPS traffic.

Registered Ports:

Registered ports range from 1024 to 49151 and are used for applications that are registered with IANA. These ports can be used by anyone, but it is recommended that they are not used for services that require interoperability.

Dynamic Ports:

Dynamic ports range from 49152 to 65535. These ports are not assigned to any application or service and are used for temporary connections.

List Open Ports on Linux

In Linux, open ports are ports that are currently in use. It’s essential to know what ports are open on your system because it could potentially indicate that your system has an open network connection that could be accessed by an unauthorized user.

There are several methods to list open ports on Linux, including netstat, ss, lsof, nmap, and netcat.

– Netstat: Netstat (short for network statistics) is a command-line tool that shows the active network connections and their corresponding protocol.

– Ss: SS (short for socket statistics) is a similar command to netstat, but it provides more detailed information about active network connections. – Lsof: Lsof (short for list open files) shows a list of files that are currently open on the system.

It can also show the processes using those files and the ports open by those processes. – Nmap: Nmap (short for network mapper) is a powerful network scanning tool used to identify active hosts, services, and devices on a network.

It can also be used to identify open ports on a system. – Netcat: Netcat is a command-line tool that can be used to establish connections between two devices, including listing ports that are currently in use.

Ports on Linux: Endpoint of Communication

In Linux, ports are used as endpoints for communication. Ports are defined by their numbering range, and they fall into three categories: well-known, registered, and dynamic ports.

Well-Known Ports:

The well-known port range, as we’ve learned, includes port numbers from 0 to 1023. These ports are typically reserved for standard services like HTTP and HTTPS and are commonly used by web servers and web browsers.

Registered Ports:

Registered ports have numbers ranging from 1024 to 49151. These ports are used by applications and services registered with IANA.

Examples of such services include MySQL and Oracle databases.

Dynamic Ports:

The dynamic port range includes port numbers from 49152 to 65535. These ports are used for temporary connections and are selected automatically by the operating system.

List Open Ports on Linux

There are several methods to list open ports on Linux. The most common methods are netstat, ss, lsof, nmap, and netcat.

Conclusion

In conclusion, ports play a vital role in networking, as they allow devices to communicate with each other. We’ve discussed what ports are, their function, their categories, and how to list open ports on Linux.

Ensuring the security of open ports on your Linux system is essential to maintaining a stable and secure network connection. Categorization of Ports: Well-known, Registered, and Dynamic

Ports provide an essential function in networking and are categorized into three groups: Well-known, Registered, and Dynamic ports.

Each category serves a unique purpose, and they have specific ranges of numbers assigned to them.

Well-Known Ports

Well-known ports, also known as System ports, are port numbers ranging from 0 to 1023. These ports are commonly known and reserved for standard services.

For instance, port 80 is used for HTTP traffic, port 22 is used for SSH traffic, and port 443 is used for HTTPS traffic. Well-known ports are used by essential system processes and require superuser privilege to operate.

They have been assigned by IANA (Internet Assigned Numbers Authority), which maintains the list of port numbers used by various protocols.

Registered Ports

Registered ports range from 1024 to 49151 and are used for applications or services that have been registered with IANA. These ports can be used by anyone but are not guaranteed free of conflicts.

Any open-source or proprietary software applications that need to communicate using a specific port must register their use with IANA to avoid conflicts. User Ports, another name for registered ports, are for general-purpose applications.

Examples of well-known registered port assignments include port 554 (RTSP -Real-Time Streaming Protocol), port 27017 (MongoDB), and port 3306 (MySQL).

Dynamic Ports

Dynamic ports, also known as Private ports, are ports ranging from 49152 to 65535. They have been set aside for temporary connections, and they are automatically assigned by the operating system.

Dynamic ports are sometimes called ephemeral ports because they are short-lived and assigned dynamically for each new connection. The system selects an available number from the dynamic range to use for a communication channel, after which it returns the port to the pool of available ports.

This process keeps the dynamic ports available for use without having to reserve them for each application. When an application or service requires a port, it requests a dynamic port assignment from the operating system.

List Open Ports on Linux

Knowing what ports are open on a Linux system is essential for network administrators and security professionals to understand the system’s security posture and potential vulnerabilities. Here are some ways to list open ports on Linux:

Using netstat

Netstat (short for network statistics) is a command-line tool that enables the user to display active network connections and their corresponding protocol. You can use netstat to list all the open ports on a system by executing the command below:

‘$ sudo netstat -tulpn’

This command displays all the listening sockets (which are open ports) on the system.

Additionally, it shows the PID (Process ID) responsible for opening the port, whether TCP or UDP protocol is used, and the type of socket.

Using ss

SS (short for socket statistics) is another command-line tool used for displaying more detailed information about active network connections than netstat. To list open ports using ss, execute the command below:

‘$ sudo ss -lptu’

This command lists all listening ports (-l), displays the process who opened them (-p), shows the socket type (-t or -u) based on whether it is TCP or UDP, and also outputs the PID in user-friendly format.

Using lsof

Lsof (short for list open files) enables the user to show a list of files that are currently open on a system. Lsof can also show the processes using those files and, in turn, the ports open by those processes.

To display all the open ports on a system, execute the command below:

‘$ sudo lsof -i’

This command lists all the open ports with the protocol information, whether it’s TCP or UDP. It also shows the process name and user ID that has opened a particular port.

Using nmap

Nmap (short for network mapper) is a network scanning tool that allows administrators and security professionals to identify active hosts, services, and devices on a network. Nmap is also used to identify open ports on a system, which makes it ideal for security exploration.

To list open ports on a system using nmap, execute the command below:

‘$ sudo nmap -sS -p-

This command scans for all open TCP ports on the given . The -p- flag tells nmap to scan all port numbers from 0 to 65535, and the -sS tells nmap to use a TCP SYN scan to detect open ports.

Using netcat

Netcat, also known as “TCP/IP Swiss Army Knife,” is another useful tool that enables users to establish connections between two devices, including listing open ports that are currently in use. To list open ports on a system using netcat, execute the command below:

‘$ sudo netcat -zv 1-65535′

This command scans all open ports on a given by setting the range of ports to scan from 1-65535.

The output displays the port numbers are open or closed. In conclusion, ports provide a vital function in networking, allowing devices to communicate with each other.

There are three categories of ports, including well-known, registered, and dynamic. Knowing how to list open ports can help diagnose issues or detect potential security vulnerabilities.

It’s important to note this is not an exhaustive list, and there are other methods to list open ports. In conclusion, ports play a crucial role in networking, allowing devices to communicate with each other while maintaining data integrity and security.

We have discussed the three different categories of ports: well-known, registered, and dynamic ports, their ranges, and their functions. We have also covered different methods to list open ports on Linux, including netstat, ss, lsof, nmap, and netcat.

Overall, understanding ports, their categories, and how to list open ports is essential for network administrators and security professionals to maintain a stable and secure network connection. It’s crucial to ensure that open ports remain secure and free from unauthorized access, so periodic scanning and monitoring of open ports are necessary to maintain network security.

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