Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.
iperf - A TCP, UDP, and SCTP network bandwidth measurement tool
tcpdump - tcpdump is a common packet analyzer that runs under the command line.
JPerf - This project gives a better UI and new functionalities to the initial JPerf 1.
netcat - Netcat is a featured networking utility which reads and writes data across network connections...
NetStress - NetStress is a user-friendly benchmarking tool that is mostly used by networking professionals to measure the network performance of both wired and wireless connections.