Security　is　the　most　important　issue　in　a　network　system.　Administrators　can　more　easily　understand　threats　to　the　network　by　using　a　model.　In　this　paper,　we　present　an　approach　for　modelling　a　network　that　considers　the　benefits　of　the　network　as　well　as　its　limitations.　In　our　approach,　we　model　the　system　as　an　optimization　problem,　which　is　solved　using　three　algorithms.　As　the　proposed　approach　is　stochastic,　it　works　very　efficiently　in　a　network　environment.　This　paper,　presents　a　mathematical　model　of　the　system.　Model　provides　easy　comprehend　of　system.　Presented　model　is　based　on　multi-objective　optimization　problem.　One　parameter　in　the　presented　model　is　security　and　another　parameter　is　user　productivity.　Security　is　the　most　important　issue　in　a　network　system.　Administrators　can　more　easily　understand　threats　to　the　network　by　using　a　model.　In　this　paper,　we　present　an　approach　for　modelling　a　network　that　considers　the　benefits　of　the　network　as　well　as　its　limitations.