We recently showcased 10 great free network management tools. Readers responded with some of their own favourites, so I'm going to take a look at those tools and report on their capabilities and usage from my perspective as an experienced network manager.

But first, let's address security. Readers mentioned the possible security implications of downloading free tools, which is a valid concern. What's to stop a coder from producing a neat network administration tool that secretly sends information about your network to a collection point for exploitation at a later date?

That's why it's a good idea to only download applications from valid sites - such as SnapFiles.com and Download.com - that test applications before releasing them - or from open-source sites such as SourceForge.net. Sometimes, such as in the case of Multi Router Traffic Grapher, the application is so widely used that it can be assumed that it's safe simply by virtue of its popularity; if the tool had a problem, someone would have found it.

No matter what, never install an application that has the ability to cut into and examine your network without understanding what it does and doesn't do. Some applications ask you to enter an administrative username and password or a Simple Network Management Protocol (SNMP) community name so they can probe deeper into certain devices. Others aggressively scan the network to the point where security devices -- and other administrators - may detect the scan and classify it as an attack. Try these in a safe environment (test network or DMZ) and use a free sniffer like Wireshark to verify what the application is doing before deploying it in a production environment.

Also, some readers noted that "freeware" applications aren't always completely free. Some applications are open source and designed as part of a greater good, which elicits input from users to make the applications better. In the case of ZipTie, that would mean plug-ins for currently unsupported network equipment. Other freeware applications are self-supporting via ad sales. Other freeware vendors hope that if you like their free version, you'll purchase the "platinum" version with bells and whistles and the ability to slice bread.

So with those caveats in mind, let's take a look at readers' favourite free network tools.

Note that I only include Windows tools. Some readers suggested Linux tools, but not everyone can afford the time to learn Linux just to evaluate a useful tool. Also, some of these tools, such as Nessus, can run on both Linux and other operating systems. And if you're really into Linux, you can read my previous article "Linux primer for networkers."

Wireshark

To be fair, Wireshark was mentioned in the original article as one of those tools that's so popular that including it in the original top 10 network tools would be essentially repeating old news. Some readers believed, however, that Wireshark is so good it deserved a mention.

Wireshark is a network protocol analyzer or sniffer and is the continuation of the well-known Ethereal project. A protocol analyzer "listens" to a network, records all of the packets seen on the connection and presents a detailed analysis of those captured packets. Properly placed, a good sniffer can provide reams of data invaluable for network troubleshooting and monitoring.

The problem is in the presentation of the information. Simply producing a text file of raw packet output is difficult to analyze. A good protocol analyzer needs to be able to take that information and present it to a network administrator in a summary format, and Wireshark does that.

Wireshark can provide deep inspection of hundreds of protocols, and more are added with each release. It can also import traces from other programs (tcpdump, Cisco IDS, Microsoft Network Monitor and Network General to name a few) so analyzing information from other sources is a breeze. It runs on Windows, Linux, Mac OS and other operating systems.

If you are going to administer a network, big or small, a protocol analyzer is a necessary tool. Wireshark fits the bill.