Monitoring your network can be a real pain. First and foremost, what tool should you use? Everyone you ask will give you a different answer. Each answer will reflect a different set of requirements and, in some cases, fill completely different needs. Here are the five network monitors I prefer, based on two criteria: They're free (as in cost) and easy to use. You might not agree with the choices, but at the price point, you'd be hard pressed to find better solutions.
1: WiresharkWireshark (Figure A) has always been my go-to monitor. When most other monitors fail to find what I want, Wireshark doesn't let me down. Wireshark is a cross-platform analyzer that does deep inspection of hundreds of protocols. It does live capture and capture save (for offline browsing), which can be viewed in GUI or tty mode. Wireshark also does VoIP analysis and can read/write many capture formats (tcpdump, Pcap NG, Catapult DCT2000, Cisco Secure IDS iplog, Microsoft Network Monitor, and many more).
2: Angry IP ScannerAngry IP Scanner (Figure B) is one of the easiest to use of all the IP scanners. It has a user-friendly GUI that can scan IP addresses (and their ports) in any range. Angry IP Scanner is cross platform and doesn't require installation, so you can use it as a portable scanner. It can get NetBIOS information, favorite IP address range, Web server detection, customizable openers, and much more. This little scanner makes use of mutlithreads, so it's going to be fairly fast. Source code is available on the download page.
3: ZenmapZenmap (Figure C) is a graphical front end to the cross-platform Nmap tool. Nmap can scan huge networks, is portable, free, and well documented. It's one of the most powerful IP traffic monitors, but that power comes with a price: complexity. Zenmap takes Nmap and makes it more accessible to users who prefer to avoid the command line. That does not mean Zenmap is the easiest of the lot. You still need to use some commands. But Zenmap offers a powerful wizard-like tool to help you through the process.
4: Colasoft Capsa FreeIf you're an admin used to more Windows-like tools, Capsa Free (Figure D) might be the perfect tool for you. There are actually two versions of Capsa: paid and free. The free version should be enough in most cases. It provides an easy-to-use dashboard you can use to create various types of captures. Capsa Free also offers plenty of alarm configurations so you can be alerted when something occurs. And it can capture more than 300 network protocols, so you won't be missing out on anything with this free tool.
5: EtherApeEtherApe is a Linux-only tool and is molded after the classic etherman monitor. It's unique in that it offers an easy-to-use mapping of IP traffic on your network. It does this in real time and gives you a clear picture of the overall look of your network traffic. You can create filters (using pcap syntax) to make reading the map easier. As you can see in Figure E, a busy network can get rather challenging to read. EtherApe will display both the node and link color with the most-used protocol so it's easier to take a quick glance, even on a busy network.
A lot of networking monitoring tools are out there, and some of them do more auditing than the tools listed here. But when you really need to know what's going on with your network, one of the above tools will do a great job.
Have you used any of these tools? What other free scanners have you tried?
Jack Wallen is an award-winning writer for TechRepublic and Linux.com. He’s an avid promoter of open source and the voice of The Android Expert. For more news about Jack Wallen, visit his website getjackd.net.