Like Nagios, Icinga can be used to monitor anything that speaks IP, as deep as you can go with SNMP and custom plug-ins and add-ons.
There are several Web UIs for Icinga, and one major differentiator from Nagios is the configuration, which can be done via the Web UI rather than through configuration files. For those who'd rather manage their configurations outside of the command line, this is a significant benefit.
Icinga integrates with a variety of graphing and monitoring packages such as PNP4Nagios, inGraph, and Graphite, providing solid performance visualizations. Icinga also has extended reporting capabilities.
If you've ever had to search for a device on your network by telnetting into switches and doing MAC address lookups, or you simply wish you could tell where a certain device is physically located (or, perhaps more important, where it was located), then you should take a good look at NeDi.
NeDi is a LAMP application that regularly walks the MAC address and ARP tables on your network switches, cataloging every device it discovers in a local database. It's not as well-known as some other projects, but it can be a very handy tool in corporate networks where devices are moving around constantly.
You can log into the NeDi Web GUI and conduct searches to determine the switch, switch port, or wireless AP of any device by MAC address, IP address, or DNS name. NeDi collects as much information as possible from every network device it encounters, pulling serial numbers, firmware and software versions, current temps, module configurations, and so forth. You can even use NeDi to flag MAC addresses of devices that are missing or stolen. If they appear on the network again, NeDi will let you know.
Discovery runs from cron at set intervals. Configuration is straightforward, with a single config file that allows for a significant amount of customization, including the ability to skip devices based on regular expressions or network-border definitions. You can even include seed lists of devices to query if the network is separated by undiscoverable boundaries, as in the case of an MPLS network. NeDi usually uses Cisco Discovery Protocol or Link Layer Discovery Protocol, discovering new switches and routers as it rolls through the network, then connecting to them to collect their information. Once the initial configuration has been set, running a discovery is fairly quick.
NeDi integrates with Cacti to some degree, and if provided with the credentials to a functional Cacti installation, device discoveries will link to the associated Cacti graphs for that device.
The Ntop project -- now known as Ntopng, for "next generation" -- has come a long way over the past decade. Call it Ntop or Ntopng, what you get is a top-notch network traffic monitor married to a fast and simple Web GUI. It's written in C and completely self-contained. You run a single process configured to watch a specific network interface, and that's about all there is to it.
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