Nmap Best Practices

In: #security
What is Nmap?

Nmap is one of the most popular free network scanning tools available on the market today. For many years, the software has become a core program for network administrators and IT professionals who want to map out their network and conduct a wide range of network inventories. It also allows the user to find live hosts on their network systems and scan for open ports and operating systems. 

Nmap runs around a command that is similar to Windows Command Prompt. However, a GUI interface is readily available for experienced users. When using Nmap for network scanning, the user will only enter commands and run scripts through the text-driven interface. They will be able to navigate through routers, firewalls, IP filters and other systems. At its core, Nmap was created for enterprise-scale networks and can scan thousands of linked devices. 

Some of Nmap’s main features include ping sweeps, OS detection and version detection. The program works by using IP packets to identify available hosts on a network as well as the services and operating systems they run. Nmap can be used on different operating systems which include Free BSF, Gentoo and Linux. Nmap also has a vibrant and active user support community.  

Network Analysis and Packet Sniffing with Nmap

Network scanning tools such as Nmap are essential for many reasons. They can detect attackers and test for vulnerabilities that are in the network. When it comes to cyber security, the more you know about packet traffic, the better you will be ready for attack and prevention against vulnerabilities. As a system administrator or network administrator, actively scanning your network is the best way to prepare against potential attacks. 

As a network scanner, Nmap is versatile. For instance, it allows the user to carry any IP active on their network. If you spot an IP that you have not seen before, you can run an IP scan in order to know whether it’s an outside attack or a legitimate service.

Additionally, Nmap is the go-to network scanning tool for many IT administrators because it offers a wide range of functionalities for free.

Nmap Use Cases

For instance, you can use Nmap to:

  • Identify open ports on your network.
  • Identify live hosts on your network.
  • Address vulnerabilities in your network infrastructure.
  • Identify the operating system of services on your network.
Understanding Nmap Port States

Nmap has six different port states:

Open: An open port is the one that’s always accepting TCP, UDP or SCTP connections. Open ports are what interest the IT professionals the most because they are the ones that are vulnerable to attacks. Open ports also show the available services on a network.

Closed: This is a port that receives and responds to Nmap probe packets but there is no application listening on that port. It’s used to identify that the host exists and for detecting the operating system.

Filtered: Nmap can’t determine whether the port is open because packet filtering prevents its probes from reaching the port. Filtering could come from router rules or firewalls. Most times, little information is given from filtered ports during scans as the filters can drop the probes without responding or respond with useless error messages such as destination unreachable.

Unfiltered: Port is accessible but Nmap doesn’t know if it’s open or closed. Only used in ACK scan which is used to map firewall rule sets. Other scan types can be used to identify whether the port is open.

Open/filtered: Nmap is unable to determine between open and filtered. This happens when an open port gives no response. No response could mean that the probe was dropped by a packet filter or any response is blocked.

Closed/filtered: Nmap is unable to determine whether the port is closed or filtered. Only used in the IP ID idle scan.

Host Scanning

If you would like to detect active hosts on a network, then the host scan is the most ideal way to scan the network. A host scan is used to send ARP request packets to all systems within a network. 

It will also send an ARP request to a particular IP that’s within an IP range, and then the active host will respond with an ARP packet sending its MAC address with a host message. This message will be received from all active hosts.

Nmap: An Important Network Administration Tool

If you are searching for an effective tool that allows you to target systems within your network and navigate around firewalls, Nmap is the right tool to use. Although it does not look like other network scanning tools that are available in the market, it remains a major part of many IT administrators and IT professional toolkits. Port scans and ping scans are just a small part of what this tool is capable of. 

Conclusively, as a cybersecurity expert or a professional network administrator, you need to learn more about the functionality of Nmap. You can also visit the Nmap website to access complete guides and information that can help you make the best use of the tool. It may also be easier to contact an IT expert that can help you scan your network using the Nmap tool.

Once you scan your network, you will have more confidence that your system and network are protected against vulnerabilities. You will also be able to protect your systems against risk and future threats. 

Start now and get more information about Nmap. You can also use a modern tool like Topia for safeguarding your system and network. Topia is a vulnerability management tool that helps CISOs as well IT managers makes informed security decisions.


Photo by Manki Kim on Unsplash

Written by Kent Weigle

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