tcp-ip Introduction

Networking protocols are normally developed in layers, with each layer responsible for a different facet of the communications. A protocol suite, such as TCP/IP, is the combination of different protocols at various layers. TCP/IP is normally considered to be a 4-layer system

ApplicationTelnet, FTP, e-mail, etcTransportTCP, UDPNetworkIP, ICMP, IGMPLinkdevice driver and interface card

1. The link layer, ( data-link layer or network interface layer ), normally includes the device driver in the operating system and the corresponding network interface card in the computer. Together they handle all the hardware details of physically interfacing with the cable (or whatever type of media is being used).
2. The network layer ( internet layer ) handles the movement of packets around the network. ( for example : Routing of packets ). IP (Internet Protocol), ICMP (Internet Control Message Protocol), and IGMP (Internet Group Management Protocol) provide the network layer in the TCP/IP protocol suite.
3. The transport layer provides a flow of data between two hosts, for the application layer above.
4. The application layer handles the details of the particular application.

Any system with multiple interfaces is called multihomed. A multihomed host will have multiple IP addresses: one per interface.