Socat

A utility similar to the venerable Netcat that works over a number of protocols and through a files, pipes, devices (terminal or modem, etc.), sockets (Unix, IP4, IP6 - raw, UDP, TCP), a client for SOCKS4, proxy CONNECT, or SSL, etc. It provides forking, logging, and dumping, different modes for interprocess communication, and many more options. It can be used, for example, as a TCP relay (one-shot or daemon), as a daemon-based socksifier, as a shell interface to Unix sockets, as an IP6 relay, for redirecting TCP-oriented programs to a serial line, or to establish a relatively secure environment (su and chroot) for running client or server shell scripts with network connections.

Nemesis

The Nemesis Project is designed to be a commandline-based, portable human IP stack for UNIX/Linux. The suite is broken down by protocol, and should allow for useful scripting of injected packet streams from simple shell scripts. If you enjoy Nemesis, you might also want to look at Hping as they complement each other well.

Nemesis

The Nemesis Project is designed to be a commandline-based, portable human IP stack for UNIX/Linux (and now Windows!). The suite is broken down by protocol, and should allow for useful scripting of injected packet streams from simple shell scripts. If you enjoy Nemesis, you might also want to look at Hping as they complement each other well.

Yersinia

Yersinia is a low-level protocol attack tool useful for penetration testing. It is capable of many diverse attacks over multiple protocols, such as becoming the root role in the Spanning Tree (Spanning Tree Protocol), creating virtual CDP (Cisco Discovery Protocol) neighbors, becoming the active router in a HSRP (Hot Standby Router Protocol) scenario, faking DHCP replies, and other low-level attacks.

Scapy

Scapy is a powerful interactive packet manipulation tool, packet generator, network scanner, network discovery tool, and packet sniffer. Note that Scapy is a very low-level tool—you interact with it using the Python programming language. It provides classes to interactively create packets or sets of packets, manipulate them, send them over the wire, sniff other packets from the wire, match answers and replies, and more.

Hping

This handy little utility assembles and sends custom ICMP, UDP, or TCP packets and then displays any replies. It was inspired by the ping command, but offers far more control over the probes sent. It also has a handy traceroute mode and supports IP fragmentation. Hping is particularly useful when trying to traceroute/ping/probe hosts behind a firewall that blocks attempts using the standard utilities. This often allows you to map out firewall rule sets. It is also great for learning more about TCP/IP and experimenting with IP protocols.

Netcat

This simple utility reads and writes data across TCP or UDP network connections. It is designed to be a reliable back-end tool to use directly or easily drive by other programs and scripts. At the same time, it is a feature-rich network debugging and exploration tool, since it can create almost any kind of connection you would need, including port binding to accept incoming connections.