The internet layer is a group of

internetworking Internetworking is the practice of interconnecting multiple computer networks, such that any pair of hosts in the connected networks can exchange messages irrespective of their hardware-level networking technology. The resulting system of interc ...

methods, protocols, and specifications in the

Internet protocol suite The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the sui ...

that are used to transport

network packet In telecommunications and computer networking, a network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the ''payload''. Control inform ...

s from the originating host across network boundaries; if necessary, to the destination host specified by an

IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...

. The internet layer derives its name from its function facilitating

, which is the concept of connecting multiple networks with each other through gateways. The internet layer does not include the protocols that fulfill the purpose of maintaining link states between the local nodes and that usually use protocols that are based on the framing of packets specific to the link types. Such protocols belong to the link layer. Internet-layer protocols use IP-based packets. A common design aspect in the internet layer is the

robustness principle In computing, the robustness principle is a design guideline for software that states: "be conservative in what you do, be liberal in what you accept from others". It is often reworded as: "be conservative in what you send, be liberal in what you a ...

: "Be liberal in what you accept, and conservative in what you send" as a misbehaving host can deny Internet service to many other users.

Purpose

The internet layer has three basic functions: *For outgoing packets, select the next-hop host ( gateway) and transmit the packet to this host by passing it to the appropriate link layer implementation; *For incoming packets, capture packets and pass the packet payload up to the appropriate

transport layer In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-e ...

protocol, if appropriate. *Provide error detection and diagnostic capability. In Version 4 of the Internet Protocol (

IPv4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version d ...

), 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 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. I ...

, as the communications end points, the hosts, now have to perform path MTU discovery and assure that end-to-end transmissions don't exceed the maximum discovered. In its operation, the internet layer is not responsible for reliable transmission. It provides only an ''unreliable'' service, and ''best effort'' delivery. This means that the network makes no guarantees about the proper arrival of packets. This in accordance with the

end-to-end principle The end-to-end principle is a design framework in computer networking. In networks designed according to this principle, guaranteeing certain application-specific features, such as reliability and security, requires that they reside in the commu ...

and a change from the previous protocols used on the early

ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first networks to implement the TCP/IP protocol suite. Both technologies became the technical fou ...

. Since packet delivery across diverse networks is an inherently unreliable and failure-prone operation, the burden of providing reliability was placed with the end points of a communication path, i.e., the hosts, rather than on the network. This is one of the reasons of the resiliency of the Internet against individual link failures and its proven

scalability Scalability is the property of a system to handle a growing amount of work by adding resources to the system. In an economic context, a scalable business model implies that a company can increase sales given increased resources. For example, a ...

. The function of providing reliability of service is the duty of higher level protocols, such as the

Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonl ...

(TCP) in the

. In IPv4, a

checksum A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data ...

is used to protect the header of each datagram. 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. IPv6 does not include this header checksum, instead relying on the link layer to assure data integrity for the entire packet including the checksum.

Core protocols

The primary protocols in the internet layer are the

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. ...

(IP). It is implemented in two versions,

and

. The

Internet Control Message Protocol The Internet Control Message Protocol (ICMP) is a supporting protocol in the Internet protocol suite. It is used by network devices, including routers, to send error messages and operational information indicating success or failure when commun ...

(ICMP) is primarily used for error and diagnostic functions. Different implementations exist for IPv4 and IPv6. The

Internet Group Management Protocol The Internet Group Management Protocol (IGMP) is a communications protocol used by hosts and adjacent routers on IPv4 networks to establish multicast group memberships. IGMP is an integral part of IP multicast and allows the network to direct ...

(IGMP) is used by IPv4 hosts and adjacent

IP multicast IP multicast is a method of sending Internet Protocol (IP) datagrams to a group of interested receivers in a single transmission. It is the IP-specific form of multicast and is used for streaming media and other network applications. It uses speci ...

routers to establish multicast group memberships.

Security

Internet Protocol Security (IPsec) is a suite of protocols for securing IP communications by authenticating and encrypting each IP packet in a data stream. IPsec also includes protocols for key exchange. IPsec was originally designed as a base specification in IPv6 in 1995, and later adapted to IPv4, with which it has found widespread use in securing

virtual private network A virtual private network (VPN) extends a private network across a public network and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. The b ...

Relation to OSI model

Because the internet layer of the TCP/IP model is easily compared directly with the

network layer In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers. Functions The network layer provides the means of tran ...

(layer 3) in the

Open Systems Interconnection The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications ...

(OSI) protocol stack, the internet layer is often improperly called ''network layer''.

Purpose

Core protocols

Security

Relation to OSI model

IETF standards

See also

References

External links