C. A SYN flood attack is waged by breaking the standard three-way handshake used by TCPIP

EncapsulationDeencapsulation Protocols based on the OSI model employ a mechanism called encapsulation. As the message is encapsulated at each layer, it grows in size. Encapsulation occurs as the data moves down through the OSI model layers from Application to Physical. The inverse action occurring as data moves up through the OSI model layers from the Physical to Application is known as deencap- sulation. The encapsulationdeencapsulation process is as follows: 1. The Application layer creates a message. 2. The Application layer passes the message to the Presentation layer. 3. The Presentation layer encapsulates the message by adding information to it. Information is added at the beginning of the message called a header and at the end of the message called a footer, as shown in Figure 3.2. 4. The process of passing the message down and adding layer-specific information continues until the message reaches the Physical layer. 5. At the Physical layer, the message is converted into electrical impulses that represent bits and is transmitted over the physical connection. 6. The receiving computer captures the bits from the physical connection and re-creates the message in the Physical layer. 7. The Physical layer strips off its information and sends the message up to the Data Link layer. 8. The Data Link layer strips its information off and sends the message up to the Network layer. 9. This process of deencapsulation is performed until the message reaches the Application layer. 10. When the message reaches the Application layer, the data in the message is sent to the intended software recipient. The information removed by each layer contains instructions, checksums, and so on that can only be understood by the peer layer that originally added or created the information see Figure 3.3. This information is what creates the logical channel that enables peer layers on different com- puters to communicate. F I G U R E 3 . 2 A representation of OSI model encapsulation Application Presentation Session Transport Network Data Link Physical DATA Header Footer DATA DATA DATA DATA DATA DATA