A protocol is a set of formal rules describing how to transmit data, especially across a network.

Protocols are:
- Rules for successful communication between different systems.
- Prearranged specifications for actions and responses.
- Designed to avoid implementation dependence and ambiguity.
- Designed to recover gracefully from errors.
- A perpetual attack target.

A classic example is the TCP Three-Way Handshake: a sender sends a SYN segment; the receiver replies with SYN/ACK; the sender completes the exchange with ACK. This establishes a reliable, bidirectional communication channel.

From a forensic perspective, protocols are not just rules to be followed; they are guidelines that attackers may bend, break, or abuse to smuggle data, bypass firewalls, evade authentication, or conduct denial-of-service attacks.

Standards bodies such as the IETF, ISO, and IEEE publish protocol specifications in minute detail. Despite this, mismatches, ambiguities, and implementation bugs remain common sources of vulnerability.