Relation To OSI Model
The internet layer of the TCP/IP model is often compared directly with the network layer (layer 3) in the Open Systems Interconnection (OSI) protocol stack. Although they have some overlap, these layering models represent different classification methods. In particular, the allowed characteristics of protocols (e.g., whether they are connection-oriented or connection-less) placed in these layers are different between the models. OSI's network layer is a "catch-all" layer for all protocols that facilitate network functionality. The internet layer, on the other hand, is specifically a suite of protocols that facilitate internetworking using the Internet Protocol.
Because of this, the OSI network layer is often described to include protocols such as the Address Resolution Protocol (ARP) which was placed in link layer by the original TCP/IP architects (RFC 1122, RFC 1123).
Strict comparison between the TCP/IP model and the OSI model should be avoided. Layering in TCP/IP is not a principal design criterion and is in general considered to be harmful (RFC 3439, section 3: "Layering Considered Harmful").
Despite clear primary references (see References below) and normative standards documents, the internet layer is still sometimes improperly called network layer, in analogy to the OSI model.
Read more about this topic: Internet Layer
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