Network Discovery

Using Zenmap

Download and install Zenmap for your platform. I use Zenmap on Linux, macOS, and Windows and have found that they all look and work the same, so there is no particular platform advantage. As the Zenmap documentation states, when installing on Windows, you might want to download and install the latest version of Npcap, rather than to rely on the one bundled with Zenmap.

Launch Zenmap and look at the interface (Figure 1).

Figure 1: Zenmap with default settings.

Zenmap’s default scan setting is Intense Scan, and the command-line equivalent of that command is shown in the Command field. You only have to supply a target for the scan. The target can be a single host, a network, or a web address. For an initial test, select an IP address or a hostname on your network, enter it into the Target field, and click Scan. It will take a few minutes for the scan to complete.

While that Intense scan runs, let’s take a closer look at it. In the Command field, you see nmap –T4 –A –v <hostname or IPaddress>.

The –T4 parameter is a timing template, and 4 is the level (aggressive). The levels range from 0 to 5 (see Table 1).

  

Table 1: Timing Template Levels

0

Paranoid

1

Sneaky

2

Polite

3

Normal

4

Aggressive

5

Insane

  

Timing values in the 0-2 range are less likely to set off network IDS alarms; they also take a long time to run, especially if the network is large. Even segmented /22 networks can take hours to scan and that’s not realistic for everyday security scanning. The documentation recommends level 4, which is right for most authorized network scans on today’s faster (1GbE) networks.

The –A option is an aggressive scan that includes other options such as OS detection, version scanning, script scanning, and traceroute. There is no need to add these options if you use –A. This option is not recommended when you want to scan a network with a bit of stealth. And the standard is -v (verbose mode), which you definitely want regardless of your scan purpose to acquire the most information possible about your target or targets.

Figure 2 shows the results of my scan of a Windows 10 system.

Figure 2: Intense scan results of a Windows 10 system.

However, Figure 3 specifically calls out the most important data for this scan: open ports and their versions. Focus on the 445/tcp line that gives you the information you need for security purposes: Windows 10 Pro 17134. This information is significant, because it tells you, with a little googling, that this system is out of date and could have multiple common vulnerabilities. For the hacker, this information is gold, because it tells them that the system administrator or system owner is not particularly diligent with updates.

Figure 3: Open ports with version numbers.

Taking a wider tour of Zenmap, you’ll see multiple tabs (Figure 4): Nmap OutputPorts/HostsTopologyHost Details, and Scans. Of those, Ports/Hosts and Host Details are the most interesting.

The Ports/Hosts tab reveals a more human-readable format than you saw on the Nmap Output tab in Figures 2 and 3.

Figure 4: The Ports/Hosts tab showing a detailed inventory of open ports.

The Host Details tab (Figure 5) reveals more information, although it is not necessarily 100 percent accurate. For example, the scanned system is a Windows 7 Pro computer upgraded to Windows 10 Pro, but identified as Server 2008 SP1 or Server 2008 R2, with an 86 percent confidence level of accuracy.

Figure 5: Host details for a Windows 10 Pro system.

Although Nmap misidentifies the system on this tab, the Ports/Hosts tab gave an accurate assessment of TCP port 445: Windows 10 Pro 17134.

Scanning Profiles

Zenmap allows you to save your scans so that you can refer to them later, and you can compare scans from two different times. Profiles are one of Zenmap's most compelling features. From the top menu, click Profile, and select New Profile or Command.

You’re presented with a new Profile Editor screen (Figure 6) that allows you to select from dozens of options. From the Scan tab, you can select TCP scan, Non-TCP scans, and Timing template, in addition to other options under the PingScriptingTargetSourceOther, and Timing tabs..

Figure 6: Zenmap Profile Editor Scan options tab.

Once you’ve saved the Profile, you can use it to scan at any future time by selecting it from the Profile drop-down list. You can selectively edit the Profile or save the changes as a new Profile. The Profile Editor requires that you name a new Profile or you have to Cancel and lose your changes.

Summary

Zenmap and Nmap are cross-platform tools that are essential for security professionals, as well as any system administrator with security responsibilities. This article provides a very brief scratch-the-surface overview of Zenmap. Zenmap is a professional security tool that provides you with a great deal of information about your network and its components. You can detect open ports, operating systems, and service versions with it. It is a powerful tool for hackers as well, which is why its use is often scrutinized and frowned upon in some settings.

No tool is perfect, but Nmap and Zenmap come pretty close to the perfect network discovery tools. They’re free and open source, which pushes them even closer to perfection. But remember that a tool and a weapon are often only separated by the intent with which they are used. With great power comes great responsibility.

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