In internet IPv4 and IPv6 protocols are at the network layer. To exchange the packet at the network layer with security aspects IPSec is used. IPSec uses to transport and tunnel mode for secure communication between the two devices. Transport mode kept the packet header as it is but encrypts the data while in tunnel mode one packet is kept in another packet for the confidentiality of the message. IPSec works to protect the data flow in host-to-host, network-to-network, and network-to-host as well. Here the paper describes the IPSec policy. In this paper, we discuss at network layer how security architecture used for protecting the secrecy and integrity of Internet traffic.