netsniff-ng is a high performance Linux network sniffer for packet inspection.
Basically, it is similar to tcpdump, but it doesn't need syscalls for fetching
packets. Instead, it uses an memory mapped area within kernel space for
accessing packets without the need of copying them to userspace ('zero-copy'
mechanism). It can be used for protocol analysis and reverse engineering,
network debugging, measurement of performance throughput, or network statistics
creation of incoming packets on central network nodes like routers or
firewalls.

The netsniff-ng toolkit consists of the following utilities:

* netsniff-ng, a fast zero-copy analyzer, pcap capturing and replaying tool
* trafgen, a multithreaded low-level zero-copy network packet generator
* mausezahn, high-level packet generator for HW/SW appliances with Cisco-CLI
* bpfc, a Berkeley Packet Filter compiler, Linux BPF JIT disassembler
* ifpps, a top-like kernel networking statistics tool
* flowtop, a top-like netfilter connection tracking tool
* curvetun, a lightweight curve25519-based IP tunnel
* astraceroute, an autonomous system (AS) trace route utility