Networking Fundamentals Practice Question 3: TCP Three Way Handshake
Networking Fundamentals · Test 1 · question 3 of 10
A junior sysadmin opens a packet capture of a browser connecting to a web server over TCP. Before any HTTP data appears, three segments set up the connection. In what order do they appear?
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Answer:
The TCP three-way handshake is started by the side opening the connection, which here is the browser (client). The server is in the LISTEN state.
1. The client sends a SYN with its initial sequence number. 2. The server acknowledges it and sends its own SYN in the same segment: SYN-ACK. 3. The client acknowledges the server's sequence number with an ACK. Both sides are now ESTABLISHED and data can flow.
So A is correct.
- B is wrong because the server's reply must carry its own SYN as well as the ACK. A bare ACK would leave the server's sequence number unsynchronized, and a client never sends a SYN-ACK as the third step. - C reverses the roles. A web server listens for connections; the client initiates them. - D is wrong because an ACK can't come first: there is nothing to acknowledge until a SYN has been received.
Reference: RFC 9293 - Transmission Control Protocol, section 3.5 (Figure 6)