SUBJECT: Security and the OSI Model
The Open Systems Interconnect (OSI) Model is the basis on which network communications function. Every network application more or less adheres to the standards of the OSI Model. Each layer of the OSI model represents a level of network functionality. For each layer, there are different types of security to protect the network at that layer.
The physical layer is the actual medium in which the data travels. This is usually a wire, hub, or over the air. The physical layer can be secured by protecting access to network cables and ports. Data transmitted over fiber optics is much harder to intercept than data being transmitted over copper wire.
The data link layer establishes the connection for the physical layer and turns the data from higher layers into the bits that will be transmitted across the medium. Security for the data link layer can be accomplished with port security, MAC address filtering, and wireless encryption.
The network layer is the layer that most people think of when it comes to network security. Network firewalls operate by blocking IP addresses which are network layer characteristics. Routers are configured to provide network layer security as well. Any security feature that allows or denies access based on IP address is a level 3 security device.
For the top 4 layers of the OSI model security and protocols don't always fall under a single layer. The transport layer plays a major part with SSL and of course TLS (Transport Layer Security). These protocols use encryption and keys to ensure private connections.
Communication sessions between hosts are established and terminated at the session layer. There is no security feature directly associated with the session layer exclusively. The protocols for FTP, SMTP, and HTTP take place at the session layer. TCP port numbers are assigned at the session layer and some routers and firewalls...