Reader favorites: 10 great free network tools

From sniffing to mapping to monitoring, these utilities perform surprisingly sophisticated tasks

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If your network infrastructure permits such, Nessus can run on anyone's machine.

If you don't have the infrastructure to protect against scans, and if you have public access ports, beware; finding a vulnerability can be as easy as an intruder running Nessus on your net. The same advice applies here as for Nmap: run it before the hackers do.

PuTTY

It wasn't too long ago that managing network devices via Telnet was commonplace. Telnet, that venerable terminal emulation program, was the first main link between the old hard-wired terminals of the mainframe days and a distributed networked environment. Yet Telnet, in all its glory, has one major problem that makes it unsuitable to remote access today: it's unencrypted.

PuTTY is a small program but big on options for secure access to your network equipment and servers running an SSH daemon.

PuTTY is a small program but big on options for secure access to your network equipment and servers running an SSH daemon.

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Enter PuTTY, a free SSH client for Windows platforms. It provides for encrypted command-line interface access to network equipment running an SSH server. For those older devices that will only respond to Telnet, there is a Telnet option as well.

PuTTY is a small program but big on options for secure access to your network equipment and servers running an SSH daemon.

As with many other terminal emulators, PuTTY allows for logging of sessions. You can save your session settings as well. Also available with the package is a secure FTP client for transferring files encrypted and an RSA and DSA key generation utility.

PuTTY is one of those rare small freeware packages with huge benefits. It should be the first tool on your networker's USB stick (everyone has one, right?) if you have a need for secure access to network equipment or secure file transfers, as you will use it often.

And a couple of the author's favorites

Our readers had several good suggestions for tools, but to round out your tool kit, here are a few more utilities I have found to be indispensable over the years.

Active Ports

Active Ports does what many of these tools do: take information available elsewhere and present it in a format that is easily accessible and understandable -- two important considerations for a network administrator tracking problems.

Active Ports does what many of these tools do: take information available elsewhere and present it in a format that is easily accessible and understandable -- two important considerations for a network administrator tracking problems.

Click to view larger image

Active Ports is a small utility designed to show -- in real time -- what processes have what ports open on a machine. The processes are linked by program, making this a very handy tool for discovering programs using network resources that might not be obvious.

There isn't much to Active Ports. Running it produces a window showing the active (open) TCP and UDP ports on the user's system. True, you can get most of this information via the netstat command, but the difference here is easily finding the program that opened the connection.

Active Ports does what many of these tools do: take information available elsewhere and present it in a format that is easily accessible and understandable -- two important considerations for a network administrator tracking problems.

Suppose you performed an analysis on your network with Wireshark because your Internet connection usage had suddenly spiked, and Wireshark showed that 95% of your bandwidth was used by one machine on your network listening on a specific TCP port. Or perhaps you performed a proactive Nmap scan and found that several machines on your network were listening on a specific TCP port. You would need to know what process has opened that port to be able to solve the root cause of the problems. Running Active Ports on a machine provides that valuable information instantly.

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