IoT, which is closely connected with our daily life, shows high growth in the automotive, healthcare, and retail fields. IoT security threats can cause severe problems in our lives. However, the security of the IoT network is insufficient to cope with security threats. Therefore, an attacker can use man-in-the-middle-attacks (MITM), DNS manipulation, and route tampering for eavesdropping, privacy breach, service outages and delay, power consumption, and system manipulation. Currently, VPN and data encryption is applied to protect the IoT network from these security threats. However, due to the limited resources of IoT device, the TCP/IP-based VPN and encryption are also limited. Although a lightweight IoT communication protocol such as LoWPAN is used, TCP/IP-based VPN such as IPsec, OpenVPN, and Wireguard require bandwidth, CPU/memory, and electric power at the level of general endpoint devices. In this paper, we propose a secure and scalable IoT (SSI) network platform that can prevent security threats while minimizing use of computing resources of an IoT device. SSI, which has a lower load than TCP/IP-based VPN, is a layer 2 VPN and supply data link frame encryption. L2TP and VXLAN are provided for a scalable layer 2 VPN, and the MACsec algorithm encrypts layer 2 frames. SSI shows 30% network speed improvement and 31.6% CPU usage reduction compared to IoT network applied OpenVPN.