Page 772 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

and UDP port 162 is used by the management console to receive

responses and notifications (also known as trap messages). Trap
messages inform the management console when an event or
threshold violation occurs on a monitored system.

Implications of Multilayer Protocols

As you can see from the previous sections, TCP/IP as a protocol suite
comprises dozens of individual protocols spread across the various
protocol stack layers. TCP/IP is therefore a multilayer protocol.
TCP/IP derives several benefits from its multilayer design, specifically
in relation to its mechanism of encapsulation. For example, when
communicating between a web server and a web browser over a typical

network connection, HTTP is encapsulated in TCP, which in turn is
encapsulated in IP, which is in turn encapsulated in Ethernet. This
could be presented as follows:

[ Ethernet [ IP [ TCP [ HTTP ] ] ] ]

However, this is not the extent of TCP/IP’s encapsulation support. It is
also possible to add additional layers of encapsulation. For example,
adding SSL/TLS encryption to the communication would insert a new

encapsulation between HTTP and TCP:

[ Ethernet [ IP [ TCP [ SSL [ HTTP ] ] ] ] ]

This in turn could be further encapsulated with a Network layer
encryption such as IPSec:

[ Ethernet [ IPSec [ IP [ TCP [ SSL [ HTTP ] ] ] ] ] ]

However, encapsulation is not always implemented for benign
purposes. There are numerous covert channel communication

mechanisms that use encapsulation to hide or isolate an unauthorized
protocol inside another authorized one. For example, if a network