A **network protocol** is a set of rules used by two or more devices on a network to *describe the order of delivery and the structure of data*. Network protocols serve as instructions that come with the information in the data packet. These instructions tell the receiving device what to do with the data. Protocols are like a common language that allows devices all across the world to communicate with and understand each other. Even though network protocols perform an essential function in network communication, security analysts should still understand their associated security implications. Some protocols have vulnerabilities that malicious actors exploit. For example, a nefarious actor could use the [[Domain Name System]] (**DNS**) protocol, which resolves web addresses to IP addresses, to divert traffic from a legitimate website to a malicious website containing malware. You’ll learn more about this topic in upcoming course materials. ### Three categories of network protocols #### Communication protocols Communication protocols govern the *exchange of information* in network transmission. They dictate how the data is transmitted between devices and the timing of the communication. They also include methods to recover data lost in transit. - [[Transmission Control Protocol]] (**TCP**) - [[User Datagram Protocol]] (**UDP**) - [[Hypertext Transfer Protocol]] (**HTTP**) - [[Domain Name System]] (**DNS**) - [[Telnet]] - [[Secure shell]] (**SSH**) - [[Internet Message Access Protocol]] (**IMAP**) - [[Simple Mail Transfer Protocol]] (**SMTP**) - [[File Transfer Protocol]] (**FTP**) #### Management Protocols Management protocols are used for *monitoring and managing activity on a network*. They include protocols for error reporting and optimising performance on the network. - [[Simple Network Management Protocol]] (**SNMP**) - [[Internet Control Message Protocol]] (**ICMP**) - [[Dynamic Host Configuration Protocol]] (**DHCP**) - [[Post office protocol]] (**POP3**) #### Security Protocols Security protocols are network protocols that ensure that *data is sent and received securely* across a network. Security protocols use encryption algorithms to protect data in transit. - [[Hypertext Transfer Protocol Secure]] (**HTTPS**) - [[Secure File Transfer Protocol ]](**SFTP**) #### Other Protocols - [[Network Address Translation]] (**NAT**) - [[Address Resolution Protocol]] (**ARP**)