netsniff-ng - The packet sniffing beast

netsniff-ng is a free Linux networking toolkit, a Swiss army knife for your daily Linux network plumbing if you will. Its gain of performance is reached by zero-copy mechanisms, so that on packet reception and transmission the kernel does not need to copy packets from kernel space to user space and vice versa.

netsniff-ng is a fast network analyzer based on packet mmap(2) mechanisms. It can record pcap files to disc, replay them and also do an offline and online analysis. Capturing, analysis or replay of raw 802.11 frames are supported as well. pcap files are also compatible with tcpdump or Wireshark traces. netsniff-ng processes those pcap traces either in scatter-gather I/O or by mmap(2) I/O.