What is a set of rules called that two or more computers must follow to communicate on network?

What is a network protocol?

A network protocol is a set of established rules that dictate how to format, transmit and receive data so that computer network devices -- from servers and routers to endpoints -- can communicate, regardless of the differences in their underlying infrastructures, designs or standards.

To successfully send and receive information, devices on both sides of a communication exchange must accept and follow protocol conventions. In networking, support for protocols can be built into software, hardware or both.

Without computing protocols, computers and other devices would not know how to engage with each other. As a result, except for specialty networks built around a specific architecture, few networks would be able to function, and the internet as we know it wouldn't exist. Virtually all network end users rely on network protocols for connectivity.

How network protocols work

Network protocols break larger processes into discrete, narrowly defined functions and tasks across every level of the network. In the standard model, known as the Open Systems Interconnection (OSI) model, one or more network protocols govern activities at each layer in the telecommunication exchange. Lower layers deal with data transport, while the upper layers in the OSI model deal with software and applications.

A set of cooperating network protocols is called a protocol suite. The Transmission Control Protocol/Internet Protocol (TCP/IP) suite, which is typically used in client-server models, includes numerous protocols across layers -- such as the data, network, transport and application layers -- working together to enable internet connectivity. These include the following:

• TCP, which uses a set of rules to exchange messages with other internet points at the information packet level;
• User Datagram Protocol, or UDP, which acts as an alternative communication protocol to TCP and is used to establish low-latency and loss-tolerating connections between applications and the internet;
• IP, which uses a set of rules to send and receive messages at the level of IP addresses; and
• additional network protocols, including Hypertext Transfer Protocol (HTTP) and File Transfer Protocol (FTP), each of which has defined sets of rules to exchange and display information.

Every packet transmitted and received over a network contains binary data. Most computing protocols will add a header at the beginning of each packet in order to store information about the sender and the message's intended destination. Some protocols may also include a footer at the end with additional information. Network protocols process these headers and footers as part of the data moving among devices in order to identify messages of their own kind.

Network protocols are often set forth in an industry standard -- developed, defined and published by groups such as the following:

• International Telecommunication Union, or ITU;
• Institute of Electrical and Electronics Engineers, or IEEE;
• Internet Engineering Task Force, or IETF;
• International Organization for Standardization, or ISO; and
• World Wide Web Consortium, or W3C.

Major types of network protocols

Generally speaking, there are three types of protocols in networking -- communication, such as Ethernet; management, such as Simple Mail Transfer Protocol (SMTP); and security, such as Secure Shell, or SSH.

Falling into these three broad categories are thousands of network protocols that uniformly handle an extensive variety of defined tasks, including authentication, automation, correction, compression, error handling, file retrieval, file transfer, link aggregation, routing, semantics, synchronization and syntax.

How to implement network protocols

In order for network protocols to work, they must be coded within software -- either as part of the computer's operating system (OS) or as an application -- or implemented within the computer's hardware. Most modern OSes possess built-in software services that are prepared to implement some network protocols. Other applications, such as web browsers, are designed with software libraries that support the protocols necessary for the application to function. In addition, TCP/IP and routing protocol support is implemented in direct hardware for enhanced performance.

Whenever a new protocol is implemented, it is added to the protocol suite. The organization of protocol suites is considered to be monolithic since all protocols are stored in the same address and build on top of one another.

What are the vulnerabilities of network protocols?

Network protocols are not designed for security. Their lack of protection can sometimes enable malicious attacks, such as eavesdropping and cache poisoning, to affect the system. The most common attack on network protocols is the advertisement of false routes, causing traffic to go through compromised hosts instead of the appropriate ones.

Network protocol analyzers are tools that protect systems against malicious activity by supplementing firewalls, antivirus programs and antispyware software.

How are network protocols used?

Network protocols are what make the modern internet possible since they enable computers to communicate across networks without users having to see or know what background operations are occurring. Some specific examples of network protocols and their uses include the following:

• Post Office Protocol 3, or POP3, is the most recent version of a standard protocol that is used for receiving incoming emails.
• SMTP is used to send and distribute outgoing emails.
• FTP is used to transfer files from one machine to another.
• Telnet is a collection of rules used to connect one system to another via a remote login. The local computer sends the request for connection, and the remote computer accepts the connection.

Other network protocol examples include the following:

• address resolution protocol, or ARP;
• Blocks Extensible Exchange Protocol, or BEEP;
• Border Gateway Protocol, or BGP;
• Binary Synchronous Communications, or BSC;
• Canonical Text Services, or CTS;
• Domain Name System, or DNS;
• Dynamic Host Configuration Protocol, or DHCP;
• Enhanced Interior Gateway Routing Protocol, or EIGRP;
• HTTP Secure, or HTTPS;
• human interface device, or HID;
• Internet Control Message Protocol, or ICMP;
• Internet Message Access Protocol, or IMAP;
• Gopher;
• Media Access Control, or MAC;
• Network News Transfer Protocol, or NNTP;
• Open Shortest Path First, or OSPF;
• Secure Sockets Layer (SSL);
• Simple Network Management Protocol, or SNMP;
• Thread;
• Transport Layer Security (TLS);
• Universal Description, Discovery and Integration, or UDDI;
• voice over IP, or VoIP; and
• X10.

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