Reader favorites: 10 great free network tools

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

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NetStumbler

If you manage wireless networks and have never used NetStumbler, you need to. NetStumbler is, at the core, an interface between what your 802.11 wireless card "sees" and what you see. It presents all of the wireless networks found in different formats, including individual transmitter signal strength or aggregate information grouped by Service Set Identifier channel or whether the network is secured or "open."

NetStumbler is the de facto tool for war drivers, as it easily identifies networks within range of a client. War drivers look for open wireless networks, and a corporate network that has improperly configured and/or installed wireless access points is ripe for exploitation. NetStumbler is a cheap tool for conducting surveys to find these potential network entry points.

NetStumbler displays signal strength of access points it

NetStumbler displays signal strength of access points it "sees," including this rogue on Channel 6.

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What about strength of signal surveys? Do you have one of those "regular" help desk callers who insists that the wireless network always becomes hard to use at a certain time of day? Take a laptop with NetStumbler and let it run unattended (in a secured location, of course) on site. You'll have a real-time log of signal strength data for troubleshooting. At least you can conclusively show if there is a drop in your access point's signal -- or a drop in connectivity from interference associated with that 2:30 p.m. nuking of a burrito in the local (and leaky) microwave.

There's a reason why NetStumbler has been around for so long. It works, and it's useful. Anyone who manages a wireless network, or even those looking for a Wi-Fi hot spot, needs NetStumbler.

Nessus

The Nessus start-up screen is simple and intuitive. Unlike old command-line versions of Nessus, which required knowledge of specific flags to set, the GUI allows for powerful vulnerability scans to be accomplished at a click of a mouse.

The Nessus start-up screen is simple and intuitive. Unlike old command-line versions of Nessus, which required knowledge of specific flags to set, the GUI allows for powerful vulnerability scans to be accomplished at a click of a mouse.

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Nessus has been one of the staples of a networker's bag of free tools for years. With more than 20,000 vulnerability checks (plug-ins), Nessus is a powerhouse application no network or security administrator should be without.

Like Nmap, in the early days using Nessus with the command line was rather cumbersome and the output difficult to decipher. It also ran on Linux, so a Linux server was necessary for scanning. But this isn't your father's Nessus, as it installs and runs easily on Windows with a crisp GUI interface.

After installation, scanning can commence immediately or a regular download of updated scanning variables can be configured. There are two such plug-in feeds available: the Direct feed provides plug-ins as they become available and is available for a fee, while the Registered feed is free, but the plug-ins are available seven days after they are available for the Direct feed.

A Nessus test scan on a 24-bit IP subnet with five hosts (a standard home network) took about a half-hour from a wireless machine -- not bad for 20,000-plus tests. The vulnerability report is simple and informative, with a summary section and details available by clicking on the IP address of the desired machine.

A Nessus test scan on a 24-bit IP subnet with five hosts (a standard home network) took about a half-hour from a wireless machine -- not bad for 20,000-plus tests. The vulnerability report is simple and informative, with a summary section and details available by clicking on the IP address of the desired machine.

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Updating your scans is important, and if you don't think that changes can occur in a short period of time, think again.

I went two weeks without updating my scan information and when I ran a new scan it found more than 7MB of new information I needed to download.

So don't think that the free subscription database isn't kept up to date.

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