Which the following flags are used to establish a TCP connection? (Choose two.)

A.
PSH

B.
ACK

C.
SYN

D.
URG

E.
FIN

Explanation:
To establish a TCP connection, the three-way (or 3-step) handshake occurs:
1. 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.
2. 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.
3. 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.
Incorrect Answers:
A: The PSH flag tells the TCP stack to flush all buffers and send any outstanding data up to and including the
data that had the PSH flag set.
D: URG indicates that the urgent pointer field has a valid pointer to data that should be treated urgently and be
transmitted before non-urgent data.
E: FIN is used to indicate that the client will send no more data.

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