GIAC Foundational Cybersecurity Technologies Practice Test

In both the TCP handshake and teardown, how much data is being sent when the ACK number increases by one?

1. Zero bytes

2. Two bytes

3. One byte

4. Three bytes

The correct answer is: Zero bytes

In TCP, the acknowledgment (ACK) number is used to indicate that a sender has successfully received a certain amount of data from the other side. When the ACK number increases by one, it signifies that the receiver has confirmed the receipt of the first byte of data from the sequence. However, it does not necessarily mean that any new data is being sent along with the acknowledgment. Specifically, during the TCP handshake and teardown processes, the ACK packets serve primarily to manage connections rather than to transmit application-layer data. In these situations, when the ACK number increments, it effectively indicates that the sender is acknowledging receipt of previously sent data without transmitting any new data. Therefore, the amount of data being explicitly sent in the ACK packet itself is zero bytes, as the packet does not contain any data payload; it is simply an acknowledgment. This understanding is crucial when analyzing TCP communication, as it highlights the distinction between the acknowledgment mechanism and the actual data transmission occurring in the TCP protocol's operations.