netsniff-ng is a high performance linux network sniffer for packet inspection.
Basically, it is similar to tcpdump, but it doesn't need one syscall per
packet. Instead, it uses an memory mapped area within kernelspace for accessing
packets without copying them to userspace (zero-copy mechanism).

This tool is useful for debugging your network, measuring performance
throughput or creating network statistics of incoming packets on central
network nodes like routers or firewalls.