Which security framework operates at the network layer?

IPsec is the correct choice because it is a security framework specifically designed to protect Internet Protocol (IP) communications by authenticating and encrypting each IP packet within a communication session. It operates at the network layer of the OSI model, facilitating secure data exchange between devices over an IP network. By securing the data at the network layer, IPsec can ensure confidentiality, integrity, and authentication for all traffic traveling through the network, regardless of the application in use.

In contrast, SSL (Secure Sockets Layer) operates primarily at the transport layer, providing security for applications like web browsing and email by forming a secure tunnel between the client and the server. PAM (Pluggable Authentication Module) is an authentication framework that operates at the application layer, allowing system administrators to create their own authentication methods for various applications. SSH (Secure Shell) functions at the session layer, providing secure access and management capabilities for networked devices, primarily for remote command execution and file transfers. Each of these alternatives serves crucial roles but does not operate specifically at the network layer like IPsec does.