Free Edition of Packet Monitor.
Packet Monitor Free Edition is designed for personal and family use. It has the same interface and functions with Packet Monitor Enterprise Edition, but with a little limitation. You can freely use it to learn network analysis.
Packet analysis is so easy by using Packet Monitor. It can be setup with the hub on your network, and it will monitor all the traffic data on your network. It sniffs packets in the net communications and captures them when you need it to. It will warn you when something is happening on your network, even block them from access. It generates all the diagrams by the monitored data, and helps you to analyze the network.