Scapy
Scapy is a Python-based interactive packet manipulation program
...It is designed to allow fast packet prototyping by using default values that work.
It can easily handle most classical tasks like scanning, tracerouting, probing, unit tests, attacks or network discovery (it can replace hping, 85% of nmap, arpspoof, arp-sk, arping, tcpdump, wireshark, p0f, etc.). It also performs very well at a lot of other specific tasks that most other tools can't handle, like sending invalid frames, injecting your own 802.11 frames, combining techniques (VLAN hopping+ARP cache poisoning, VoIP decoding on WEP protected channel, ...), etc.
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