TCP establishes a connection via the THREE-WAY HANDSHAKE. The sequence of segments is
ASYN — SYN/ACK — ACK
BSYN — ACK — SYN
CFIN — FIN/ACK — ACK
DRST — RST — RST
Answer & Solution
Correct answer: A. SYN — SYN/ACK — ACK
1. TCP 3-way handshake (RFC 1180 §7):
- Client → Server: SYN (with initial sequence number $x$)
- Server → Client: SYN+ACK (server's sequence $y$, ack $x+1$)
- Client → Server: ACK (ack $y+1$)
2. After this exchange, both sides have agreed on starting sequence numbers and the connection is ESTABLISHED.
3. Option C is the CONNECTION TERMINATION sequence (FIN-based, 4-way close). Option D is the reset/abort sequence. Option B has wrong second step.
_Source: RFC 1180 "A TCP/IP Tutorial", §7 (TCP — connection establishment)._
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