A layered approach requires implementing security solutions at different spectrums of the network. Another similar concept is islands of security. To implement islands of security, do not restrict your thinking to perimeter security. Do not depend on just one method for your security. You should, instead, have layers of protection—perimeter, distribution, core, and access layer.

 

This layered approach is related to the technology of an environment and the complexity of each of the technologies at each layer. The complexity comes from different protocols, applications, hardware, and security mechanisms that work at one or more of the seven layers in the OSI model. Just as there are different levels within an environment, different types of attacks can occur at each level and would require respective countermeasures.