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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Protocol Suite and Architecture

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TCP/IP Architecture and the TCP/IP Model
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TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
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TCP/IP Protocols
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Network Layer (OSI Layer 3) Protocols

The very important network layer contains the Internet Protocol and several related and support protocols, as shown in Table 21.

Table 21: TCP/IP Protocols: Network Layer (OSI Layer 3)

Protocol Name

Protocol Abbr.


Internet Protocol, Internet Protocol Version 6

IP, IPv6

Provides encapsulation and connectionless delivery of transport layer messages over a TCP/IP network. Also responsible for addressing and routing functions.

IP Network Address Translation


Allows addresses on a private network to be automatically translated to different addresses on a public network, providing address sharing and security benefits. (Note that some people don’t consider IP NAT to be a protocol in the strict sense of that word.)

IP Security


A set of IP-related protocols that improve the security of IP transmissions.

Internet Protocol Mobility Support

Mobile IP

Resolves certain problems with IP associated with mobile devices.

Internet Control Message Protocol


A “support protocol” for IP and IPv6 that provides error-reporting and information request-and-reply capabilities to hosts.

Neighbor Discovery Protocol


A new “support protocol” for IPv6 that includes several functions performed by ARP and ICMP in conventional IP.

Routing Information Protocol, Open Shortest Path First, Gateway-to-Gateway Protocol, HELLO Protocol, Interior Gateway Routing Protocol, Enhanced Interior Gateway Routing Protocol, Border Gateway Protocol, Exterior Gateway Protocol


Protocols used to support the routing of IP datagrams and the exchange of routing information.

Host-to-Host Transport Layer (OSI Layer 4) Protocols

The transport layer contains the essential protocols TCP and UDP, as shown in Table 22.

Table 22: TCP/IP Protocols: Host-to-Host Transport Layer (OSI Layer 4)

Protocol Name

Protocol Abbr.


Transmission Control Protocol


The main transport layer protocol for TCP/IP. Establishes and manages connections between devices and ensures reliable and flow-controlled delivery of data using IP.

User Datagram Protocol


A transport protocol that can be considered a “severely stripped-down” version of TCP. It is used to send data in a simple way between application processes, without the many reliability and flow management features of TCP, but often with greater efficiency.

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