the evil bit
loresecuritynetworking
The April Fools' RFC proposing that malicious packets simply set a header bit to declare themselves evil.
Steve Bellovin's RFC 3514 (April 1, 2003) defines a security flag in the IPv4 header: benign packets set it to 0, attack packets must set it to 1, and firewalls need only drop the marked ones. It is the field's favorite satire of every product that promises to detect intent from the wire. Whenever someone proposes trusting the sender's self-declaration, an engineer will ask if it checks the evil bit.
Also known as: RFC 3514