PACKET SNIFFER : TCP DUMP

Tcpdump is the classic IP sniffer which requires fewer system resources. It is great for tracking down network problems or monitoring activity. 

Download here:

http://www.megaupload.com/?d=IGQELRZ3

PACKET SNIFFER : WIRESHARK

Wireshark is a fantastic open source network protocol analyzer for Unix and Windows. It allows you to examine data from a live network or from a capture file on disk. You can interactively browse the capture data, delving down into just the level of packet detail you need. Wireshark has several powerful features, including a rich display filter language and the ability to view the reconstructed stream of a TCP session. It also supports hundreds of protocols and media types.

Download from Wireshark Official Website:

http://www.wireshark.org/download.html

NETWORK SCANNING TOOL : NMAP

Nmap ("Network Mapper") is a free and open source utility for network exploration or security auditing. Many systems and network administrators also find it useful for tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. It was designed to rapidly scan large networks, but works fine against single hosts.

Download here (Linux Users):

http://nmap.org/dist/nmap-5.00.tar.bz2 

Download here (Windows Users):

http://nmap.org/dist/nmap-5.00-setup.exe