Local Area Networks(LAN) at present become an important instrument for organizing of process and information communication in an organization. They provides important purposes such as association of large amount of data, hardware and software resources and expanding of optimum communications. Becase these network do work with valuable information, the problem of security providing is an important issue in organization. So, the stablishment of an information security management system(ISMS) in organization is significant. In this paper, we introduce ISMS and its implementation in LAN scop. The assets of LAN and threats and vulnerabilities of these assets are identified, the risks are evaluated and techniques to reduce them and at result security establishment of the network is expressed.