Network security
Network Security

Installing firewall or anti-virus software on enterprise workstations can help prevent some of the security problems the Internet can cause; but not everything. By understanding the different Open Systems Interconnect (OSI) levels and security threats involved with each one of them, it is easier to plan a strategy to combat security problems.
Purpose and Scope
To cover all areas I have listed the network security measures that are associated with each level of the Open Systems Interconnect (OSI).
Physical layer
This layer is responsible for moving raw bits from one node to another: electrical impulse, light or radio signals. This layer represents the physical application security. It includes access control, power, fire, water, and backups. Many of the threats to security at the Physical layer cause a Denial of Service (DoS) of the enterprise application, making the application unavailable to enterprise users. To ensure this does not occur, the electrical and mechanical parts of the network are not only tested periodically but are kept safe from external damages like tampering or other physical destruction. The backups are in a secured room only few people have access to this room.
One method used to manage security in this layer is through Physical Layer Automation. By use of tools such as the Apcon's IntellaPatch™ line of copper and fiber Physical Layer switches, the network administrators have control and security at the foundation or physical layer of their network. With "wire once technology" built into every IntellaPatch switch, network administrators have the ability to manage and re-arrange the physical cabling topology of network closets or wire racks without the manual effort of pulling and patching a single wire. The network is cabled to IntellaPatch switches, then, using the graphical user interface (GUI) of Apcon's Control™ software, instantaneously configure and connect from any port to any other port without ever leaving your desk. Making changes to the network topology easy using these Apcon's IntellaPatch switches.
Security being top priority in networks, tools like IntellaPatch Physical Layer switches provide access control for both small and large networks. In large environments or multi-floor building environments where wiring termination points are scattered among various buildings or floors, managing and monitoring those facilities can be a tedious and cumbersome job. This is key for environments like manufacturing where there are multiple work shifts.

Data Link layer
At this layer data packets are encoded and decoded into bits. This layer ensures that everything sent was physically received. This layer encompasses switch security topics such as ARP attacks and MAC flooding. Simple configuration changes to the network switch can help protect enterprise applications from Data layer attacks. At my workplace only authorized users can have access to layer 2 software. The IT department has full control and determines when changes are made and who is authorized to do these changes. Other measures are taken like Shutting down unused ports in the VLAN and limiting the number of allowed MAC addresses by using port security mechanism.
Network and Transport layers
These layers handle the routing or forwarding of data. These layers are where the most common security precautions take place – this layer is where routers and firewalls are implemented. Examples of threats that occur at this level are unauthorized retrieval of endpoint identity and unauthorized access to internal systems. The company utilizes Network Address Translation, Access Control lists, and firewall technologies to mitigate these risks.
Session
This layer sets up, coordinates and terminates conversations, exchanges and dialogs between the applications at each end. This layer also sets up remote communication. At these layers the IT manager's ability to mitigate application security risks begins to diminish as developers take a bigger role in protecting applications. One way to ensure security on this layer is by testing application integrity, proper routing transaction, capability to handle messages under stress and the capability to handle incomplete transactions.
IT managers can prevent unauthorized login/password access and unauthorized data access, which are common attacks at these layers, by using encryption and authentication methods. Audit trails of all additions and deletions of user critical files and changes to their privileges should be maintained.
Presentation layers
This layer is usually part of the operating system. It converts incoming and outgoing data from one presentation format to another. For example, it converts data from text stream into a pop-up window with the newly arrived text, or from EBCDIC to ASCII. Examples of ensuring security at this layer are:
• Since this layer manipulates data, it's important to ensure that the software is authorized.
• Investigate the use of encryption, such as Secure Socket Layer (SSL).
• Review what encryption algorithm is in use and whether it's used securely and whether secure implementations are used. For instance, are you using the 40-bit encryption key for SSL or the more secure 128-bit one?
• If you are generating certificates, is the private key secure?
Application layer
This layer is where user authentication and privacy is considered. The layer supports application and end user processes. Many security protection methods are the responsibility of the programmer at this layer. Backdoor attacks occur at this level and it is the programmer's responsibility to close those doors. IT managers can use access control methods described to assist in preventing backdoor attacks. Our IT managers have setup tools such as virus scanners, Web Inspect, and intrusion detection devices to help prevent compromise of enterprise applications.
Conclusion
When looking at security issues in a company, it can be overwhelming. To be able to identify all security areas of the network it is important to look at all layers of the network. A structured way to do this is by looking at what type of security is associated with each level of the Open Systems Interconnect (OSI) Model. .

References
Data Communications http://apcon.com/ethernet.php retrieved on August 9, 05
Holl, K. (2003), SANS Security Essentials. OSI Defense in Depth to Increase Application Security, p2.