Rancang Bangun Komunikasi Internal Berbasis Voice over Internet Protocol (VoIP) dengan Pengamanan Fail2Ban terhadap Serangan Session Initiation Protocol (SIP)

Reliance on paid cellular services and third-party applications in institutional environments often causes cost inefficiency and data security risks. As a solution, this study aims to build an independent Voice over Internet Protocol (VoIP) communication infrastructure using Asterisk IP-PBX with a custom Flutter-based client application, secured from cyber attacks using the Fail2Ban Intrusion Prevention System (IPS). The system development uses the Network Development Life Cycle (NDLC) framework. Evaluations were conducted through cross-network functionality testing and security penetration testing against SIP Brute Force attacks. Functionality test results show that the client application successfully executes voice calls, WebRTC-based video calls, and instant messaging synchronization via a REST API without disruptive latency. In security testing using SIPVicious (svcrack) simulation, the system achieved a 100% success rate in detecting authentication anomalies. Fail2Ban automatically blocked the attacker's IP at the firewall (Iptables) on port 5060 within seconds. In conclusion, this research produced an internal communication ecosystem with proven reliability, measured by the seamless operation of cross-network communication features and a 100% success rate in automatically thwarting illegal access exploitation.