Which the following flags are used to establish a TCP connection? (Select TWO).
A. PSH B. ACK C. SYN D. URG E. FIN
Answer: B,C
Explanation: To establish a TCP connection, the three-way (or 3-step) handshake occurs:
SYN: The active open is performed by the client sending a SYN to the server. The client sets the segment’s sequence number to a random value A. SYN-ACK: In response, the server replies with a SYN-ACK. The acknowledgment number is set to one more than the received sequence number i.e. A+1, and the sequence number that the server chooses for the packet is another random number, B. ACK: Finally, the client sends an ACK back to the server. The sequence number is set to the received acknowledgement value i.e. A+1, and the acknowledgement number is set to one more than the received sequence number i.e. B+1.