Among the seven layers in the OSI reference model, layer 3 belongs to the network layer. There are some important network layer protocols that you should know of. Protocol is nothing but a set of rules that determine how messages are being exchanged between different computers.
Let us now briefly consider five important protocols that are related to the network layer message transfers. They are: IPv4, IPv6, CLNP, IPSec, and ICMP.
IPv4: IP stands for Internet Protocol while v4 indicates that it is the version 4. Here, version 4 refers to the fourth revision of the Internet Protocol that was later widely deployed. There exists an IPv4 header structure that is the basis for network layer transfer of packets. This is one of the most important network layer protocols.
IPv6: This is also an Internet Protocol that is of version 6. Though IPv4 is widely used these days, it is expected that this IPv6 is going to take over the rest of the attention. Hence, it is called the next generation protocol. There are just a few basic differences between both the protocols. The address space of IPv6 is larger than that of the IPv4.
CLNP: CLNP stands for Connectionless Network Protocol. The service that this protocol renders is called CLNS. This routes the messages to their destination independently.
IPSec: Internet Protocol Security is one such protocol that enables encryption and also authentication of every IP packet that moves in the data stream. Encryption and authentication are two techniques to ensure secure message transfer from the source to the destination.
ICMP: ICMP stands for Internet Control Message Protocol. This particular protocol is very important among all the network layer protocols. This is used by the operating systems of network computers to send error messages indicating that a particular service was not available or the connection to a router failed, etc.