Computer networks are very important in today�s scenario. They have changed the way we do business and the way we live. There are several protocols that help us to establish these networks. The most widely used network protocol is ARP (Address Resolution Protocol) which is used to find the physical address of the node when its internet address is known. In this paper we have discussed the weaknesses of this protocol and have proposed various methods of active detection and prevention of ARP poisoning(spoofing) based Man-in- the-Middle(MitM) attacks on switched Ethernet LAN�s, Denial-of-service (DoS), session hijacking etc. We have implemented tools and defense mechanisms such as central server on a network or subnets, encryption of data traffic etc. that help us to reduce these spoofing attacks
