14.5.6 Check Your Understanding – TCP Communication Process Answers

1. Which of the following would be valid source and destination ports for a host connecting to an email server?

  • Source: 25, Destination: 49152
  • Source: 80, Destination: 49152
  • Source: 49152, Destination: 25
  • Source: 49152, Destination: 80

Explanation: The destination port is the well-known port for Simple Mail Transport Protocol, which is 25. This is the port that the mail server will be listening on. The source port is dynamically selected by the requesting client and can be 49152.

2. Which control bit flags are used during the three-way handshake?

  • ACK and FIN
  • FIN and RESET
  • RESET and SYN
  • SYN and ACK

Explanation: The three-way handshake consists of a three message exchanges with the following control bit flags: SYN, SYN ACK, and ACK.

3. How many exchanges are needed to end both sessions between two hosts?

  • one exchange
  • two exchanges
  • three exchanges
  • four exchanges
  • five exchanges

Explanation: There are four exchanges to end both sessions between two hosts. (1) Host A sends a FIN. (2) Host B sends an ACK. (3) Host B sends a FIN. (4) Host A sends an ACK.

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