The internet layer derives its name from its function facilitating internetworking, which is the concept of connecting multiple networks with each other through gateways.
The internet layer has three basic functions: In Version 4 of the Internet Protocol (IPv4), during both transmit and receive operations, IP is capable of automatic or intentional fragmentation or defragmentation of packets, based, for example, on the maximum transmission unit (MTU) of link elements.
However, this feature has been dropped in IPv6, as the communication endpoints, the hosts, now have to perform path MTU discovery and ensure that end-to-end transmissions don't exceed the maximum discovered.
The checksum ensures that the information in a received header is accurate, however, IPv4 does not attempt to detect errors that may have occurred to the data in each packet.
IPsec was originally designed as a base specification in IPv6 in 1995,[2][3] and later adapted to IPv4, with which it has found widespread use in securing virtual private networks.