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■    TCP/IP

■    IPX/SPX

■    NetBEUI



The Transmission Control Protocol/Internet Protocol (TCP/IP) is the protocol of choice today. It, like other protocols, is used to allow two computers to communicate over a network. However, TCP/IP is used not only on local area networks, but also over wide area networks and the Internet. Actually, TCP/IP is the only protocol in use on the Internet. You’ll learn more about TCP/IP in Chapter 3, “TCP/IP Fundamentals.”


Addressing the network entities protocol (called hosts in TCP/IP parlance) that runs the TCP/IP is fairly straightforward in TCP/IP. Each host is given (either manually or automatically) a dotted decimal IP address in the format where xxx is a number from 0 to 255. There are several addressing rules, which you will learn more about in Chapter 3.

Because addressing is a Network layer concept, the protocols that deal with addressing can be found at this layer. The Address Resolution Protocol (ARP) is responsible for resolving an IP address to the MAC address of the receiving host. The MAC address is a Data Link layer address hard-coded to each network card at the manufacturer. When a TCP/IP packet is sent, at some point a router will need to determine exactly which station the packet

is intended for. On Ethernet networks, the router will use an ARP lookup and ARP broadcasts. Essentially, the router listens for the periodic ARP broadcasts from all hosts and records the information in its ARP cache (basically a table that says which IP address is associated with which MAC address). When a router receives packets and needs to send them to a particular station on one of its own segments, it examines the IP address of the destination, looks up the MAC address of that station using ARP, and forwards the packet via Ethernet to the intended destination.

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