What is a network protocol?

A network protocol is an agreed set of rules for how devices exchange data, so that equipment from different makers understands each other. Some protocols move data (TCP and UDP), some find addresses (DHCP, ARP), some translate names (DNS), some protect data (TLSTLS: Transport Layer Security. The encryption that protects most internet traffic, such as HTTPS.) and some serve specific purposes, such as SSH for remote administration, SMB for file sharing or Modbus for industrial machines. Security tools recognise protocols to understand what a connection is doing. An unexpected protocol, such as remote-administration traffic from a printer or industrial commands from an office laptop, is often a sign worth checking.

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