(1 . Higher Educati on Admissi on Committee Office of L ianyungang,L ianyungang 222006, China 2 . Modern Educati on Technique Center, Huaihai I nstitute of Technol ogy, L ianyungang 222005, China) Abstract: The outbreak ofARP cheating virus interferes with the nor mal functi oning of LAN. On the basis of thoroughly und standing of the p rinci p les, this paper analyzes the p rinci p les, pattern and classificati ons ofARP in details . And it also discu the tactics t o take strict p recauti ons ofARP fr om t wo sides— — —the administrati on ofLAN and Client Host . The pur pose of the cussi on is t o guarantee the normal running of LAN users . Key words: virus p rinci p les LAN client host