IP Calculator / IP Subnetting
ipcalc takes an IP address and netmask and calculates the resulting
Free TCP/IP Network Calculators. Includes web-based Subnet, Supernet and network / node calculators.
Wireshark is a network protocol analyzer for Unix and Windows. List of features.
Featuring link layer, IP, and TCP modes, EtherApe displays network activity graphically with a color coded protocols display. Hosts and links change in size with traffic.
ngrep (network grep) is a network packet analyzer. It runs under the command line, and relies upon the pcap library and the GNU regex library.
Cain and Abel [download]
Cain & Abel is a password recovery tool for Microsoft Operating Systems.
NetworkMiner is a Network Forensic Analysis Tool for Windows.
tcpdump is a common packet analyzer that runs under the command line.
Kismet is a console (ncurses) based 802.11 layer-2 wireless network detector, sniffer, and intrusion detection system.
Ettercap is a suite for man in the middle attacks on LAN. It features sniffing of live connections, content filtering on the fly and many other interesting tricks.
P0f is able to identify the operating system of a target host simply by examining captured packets even when the device in question is behind an overzealous packet firewall.
inSSIDer is a wireless network scanner for Windows, OS X, and Android.
Netstumbler is the best known Windows tool for finding open wireless access points (“wardriving”).
Dsniff is a set of password sniffing and network traffic analysis tools to parse different application protocols and extract relevant information. dsniff, filesnarf, mailsnarf, msgsnarf, urlsnarf, and webspy passively monitor a network for interesting data (passwords, e-mail, files, etc.).
KisMAC is a wireless network discovery tool for Mac OS X. It has a wide range of features, similar to those of Kismet
Ntop [download] limited to 2,000 packets capture
Ntop shows network usage in a way similar to what top does for processes. In interactive mode, it displays the network status on the user’s terminal.