Scapy

Scapy is a powerful interactive packet manipulation library and tool written in Python. It can forge or decode packets of a wide number of protocols, send them on the wire, capture them, match requests and replies, and much more. Unlike traditional tools that are limited to specific protocols or tasks, Scapy gives you programmatic control over every byte of every packet, making it possible to craft custom protocol implementations, build network scanners, perform protocol fuzzing, and create network testing tools from scratch. Scapy handles all common protocols (Ethernet, IP, TCP, UDP, DNS, HTTP, ARP, ICMP, 802.11, Bluetooth, and hundreds more) and can dissect captured packets into their component layers. Its interactive Python shell makes it equally useful for quick experiments and complex scripted network operations.