Fear of security breaches has been a major reason for the busniness world's reluctance to embrace the internet as a viable means of communication. This paper discusses the current security measures available for the IPv4 infrastructure. The paper is addressed to readers with a basic understanding of common security mechanisms including some kinds of attack and IPsec. The security of IP is important to the network. The paper analyses the prototypes of network attack, some possible means in IPv6 then presented. IPsec is a series of guideline for the protection of IP layer on the Internet. At the end, some kinds of attack are introduced under IPsec Mode.