Which protocol provides port-based network access control from the physical layer upwards?

The correct choice is 802.1X, which is a protocol specifically designed to provide port-based network access control. What this means is that 802.1X offers a mechanism for authenticating devices wishing to connect to a network at the point of access, effectively controlling who can join the network and under what circumstances. It operates at the data link layer (Layer 2) of the OSI model and can be implemented over wired and wireless networks.

802.1X works by using an authentication server, usually RADIUS, to verify the credentials of a device (or user) before granting access to the network. This allows network administrators to enforce security policies, ensuring that only authorized users and devices can access network resources.

In contrast, the other protocols listed do not provide this type of access control from the physical layer upwards. HTTP (Hypertext Transfer Protocol) is used for transferring web pages and does not involve network access control. FTP (File Transfer Protocol) is mainly designed for transferring files over a network and also does not handle authentication at the network access level. SNMP (Simple Network Management Protocol) is used for managing and monitoring network devices, not for controlling access to the network itself. Thus, 802.1X stands out