Wireshark
Wireshark is a free and open source packet analyzer. Originally named Ethereal, the project was renamed Wireshark. It lets you capture and interactively browse the traffic running on a computer network.
You can download Wireshark for Windows or Mac OS X from it's official website. If you’re using Linux or another UNIX-like system, you’ll probably find Wireshark in its package repositories. For example, if you’re using Ubuntu, you’ll find Wireshark in the Ubuntu Software Center.
Just a quick warning: Many organizations don’t allow Wireshark and similar tools on their networks. Don’t use this tool at work unless you have permission.
Capturing Packets
After downloading and installing Wireshark, you can launch it and click the name of an interface under Interface List to start capturing packets on that interface. For example, if you want to capture traffic on the wireless network, click your wireless interface. You can configure advanced features by clicking Capture Options, but this isn’t necessary for now.
As soon as you click the interface’s name, you’ll see the packets start to appear in real time. Wireshark captures each packet sent to or from your system. If you’re capturing on a wireless interface and have promiscuous mode enabled in your capture options, you’ll also see other the other packets on the network.
Click the stop capture button near the top left corner of the window when you want to stop capturing traffic.
