What Is Protocol ?
What is a network protocol?
In networking, a protocol is a set of rules for formatting and processing data. Network protocols are like a common language for computers. The computers within a network may use vastly different software and hardware; however, the use of protocols enables them to communicate with each other regardless.
Standardized protocols are like a common language that computers can use, similar to how two people from different parts of the world may not understand each other's native languages, but they can communicate using a shared third language. If one computer uses the Internet Protocol (IP) and a second computer does as well, they will be able to communicate — just as the United Nations relies on its 6 official languages to communicate amongst representatives from all over the globe. But if one computer uses IP and the other does not know this protocol, they will be unable to communicate.
On the Internet, there are different protocols for different types of processes. Protocols are often discussed in terms of which OSI model layer they belong to.
What are the layers of the OSI model?
The Open Systems Interconnection (OSI) model is an abstract representation of how the Internet works. It contains 7 layers, with each layer representing a different category of networking functions.
The OSI Model
Protocols make these networking functions possible. For instance, the Internet Protocol (IP) is responsible for routing data by indicating where data packets* come from and what their destination is. IP makes network-to-network communications possible. Hence, IP is considered a network layer (layer 3) protocol.
As another example, the Transmission Control Protocol (TCP) ensures that the transportation of packets of data across networks goes smoothly. Therefore, TCP is considered a transport layer (layer 4) protocol.
*A packet is a small segment of data; all data sent over a network is divided into packets.
Which protocols run on the network layer?
As described above, IP is a network layer protocol responsible for routing. But it is not the only network layer protocol.
IPsec: Internet Protocol Security (IPsec) sets up encrypted, authenticated IP connections over a virtual private network (VPN). Technically IPsec is not a protocol, but rather a collection of protocols that includes the Encapsulating Security Protocol (ESP), Authentication Header (AH), and Security Associations (SA).
ICMP: The Internet Control Message Protocol (ICMP) reports errors and provides status updates. For example, if a router is unable to deliver a packet, it will send an ICMP message back to the packet's source.
IGMP: The Internet Group Management Protocol (IGMP) sets up one-to-many network connections. IGMP helps set up multicasting, meaning multiple computers can receive data packets directed at one IP address.