Freeware has long reigned as a go-to tool for network managers. Applications such as Ethereal, Multi Router Traffic Grapher (MRTG) and Snort provide an inexpensive means to monitor devices, traffic and security in even the largest networks.

More recently, freeware’s community-supported cousins -- open source applications -- have emerged to tackle many network-monitoring tasks at no cost to their owners. Such projects as Nagios and open source products from commercial vendors GroundWork Open Source, Hyperic and Splunk have been gaining ground in enterprise IT shops.

Here, a few network managers in the know share their latest free finds:

1. DHCP_probe

Network managers tracking down unauthorized IP addresses on their networks should check out this application developed by a member of Princeton University’s IT team.

DHCP_probe “attempts to discover DHCP and BootP servers on a directly attached Ethernet network,” according to its creator, Irwin Tillman of the Network Systems Group at Princeton University’s Office of Information Technology. The application sends out requests to DHCP servers on a network, and if a nonauthorized server answers the requests, the software will alert IT staff to the server’s existence.

Rick Beebe, manager of system and network engineering for ITS-Med, says the application addresses “a regular problem” at the Yale University School of Medicine in New Haven, Conn.

“Someone will bring a Linksys or Netgear wireless access point or an Apple AirPort in and put it on the network, so they can have wireless in the office. Only they plug it in backward and start sending IP addresses to a large part of the network,” Beebe says. “Usually [devices that] get those IP addresses appear broken, because the IPs aren't actually usable, or someone attempting to share files on their machine checks the box that says ‘share my Internet’ connection, [which produces] the same result.”

Last updated in 2004, DHCP probe was first developed to run on Sun Solaris and was ported to also run on Linux. Beebe finds its function useful, but says he is surprised it hasn’t been updated to be less version-dependent and easier to deploy -- considering the problem it solves.

“I find it hard to believe that we’re the only ones with this problem so I’m surprised there hasn’t been more development of it,” he says.