In the TCP/IP model or DoD model, two main reasons exist for the Internet layer, which maps over to the OSI model's Network layer: routing and providing for a single network interface to the upper layers.
Without this layer, application programmers would need to write what are called hooks into every application for each different Network Access Protocol. If we think about it, that would mean a different version for each application—an example would be one for Ethernet and another for wireless, you get the picture. To cure this ineffective and unproductive method, we have the IP protocol, which is a single network interface for upper-layer protocols. The following is a list of the important protocols at the internet layer:
- Internet Protocol (IP)
- Internet Control Message Protocol (ICMP)
- Address Resolution Protocol (ARP)