Which protocol is designed for securing IP communications across networks at the network layer?

• A. IPsec
• B. SSL/TLS
• C. SSH
• D. PKI

Answer: (A)

Securing IP communications across networks at the network layer is achieved by IPsec. IPsec sits at the IP layer and protects the data as it travels between hosts or gateways, authenticating and optionally encrypting each IP packet. It uses mechanisms like AH for data integrity and authentication, and ESP for confidentiality, and supports both transport and tunnel modes to handle different deployment scenarios such as host-to-host or network-to-network connections. This layer-specific protection is what makes IPsec the right fit for securing IP traffic across networks. The other options operate at higher layers or serve as frameworks: SSL/TLS protects sessions at the transport/app layer (typically for web traffic), SSH provides secure remote access at the application layer, and PKI is a certificate/key management framework rather than a protocol that directly secures IP packets.