Over the past decades, Session Initiation Protocol (SIP) has achieved much attention regarding Voice over IP services(VOIP) when comparing with various protocols like H.323 or MGCP. SIP is the special protocol for present and future IP telephony services which is turning as real challenger for traditional telephony services. Due to its open architecture, the available services are vulnerable to various kinds of security threats like presently live on the Internet. Hence, there is a need to provide security to SIP based VOIP implementations, especially, a remotely secure communication using Virtual Private Networks (VPN). In this paper, we discuss about site-to-site IPsec VPN which communicate in the intra-nets. The implementation of IPsec VPN is done with security protocols for exchanging key management, authentication and integrity using Graphical Network Simulator 3 (GNS3). The encryption of data packets when information is transferred between different sites is tested and verified using tools like Ping, IPerf and Wireshark. The performance in terms of delay, bandwidth consumption, jitter and the data rate of the proposed method with and without Firewalls is analyzed. It is obvious that our proposed method can provide the security and prohibit the attackers to attack the network.
