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In the previous chapter of [[Security+ Essentials]] we looked at TCP/IP ports and the issue of nonessential services. Clearly a server with all ports blocked and all services disabled would be of little use to anyone except the system administrator sitting at the system console. The simple fact is that in order to be useful computer systems need to be able to communicate with other systems, either on a local area network (LAN) or over wide area networks (WAN) or the internet.