IPsec operates at which layer of the OSI model to secure traffic?

• A. Application layer
• B. Transport layer
• C. Network layer
• D. Data link layer

Answer: (C)

IPsec secures IP traffic by operating at the network layer. It protects IP packets themselves as they traverse an IP network, applying encryption and/or authentication to the packet (and payload) using ESP and/or AH. Because this security processing happens for IP packets (Layer 3) rather than within applications or per-connection transport, its placement is at the network layer. It sits below the transport layer (so it isn’t securing TCP/UDP connections with TLS/DTLS) and above the data link layer, and it can work in both transport and tunnel modes. Hence, the network layer is the correct choice.