Monitoring a Network

[Nermal]

My brother is using Network Spy (http://www.sumitbirla.com/network-spy/netspy.php) for Windows, which allows him to see what's happening on the network (which computers are transmitting data etc). Does anyone know of a similar app for the Mac?

[superbovine]

yeah, you will need os x with x11 installed. (that is considering you want the gui functionality)

http://www.ethereal.com/
http://www.snort.org/

[Counterfit]

MacSniffer (http://www.versiontracker.com/dyn/moreinfo/macosx/13007) does the trick, and since it's an Aqua frontend for tcpdump, you don't need X11.