Skip to content
GATEiit

GATE CSE 2021 Set 2 Q17: TCP SYN-ACK segment in the three-way handshake

Question

Consider the three-way handshake mechanism followed during TCP connection establishment between hosts P and Q. Let X and Y be two random 32-bit starting sequence numbers chosen by P and Q respectively. Suppose P sends a TCP connection request message to Q with a TCP segment having SYN bit = 1, SEQ number = X, and ACK bit = 0. Suppose Q accepts the connection request. Which one of the following choices represents the information present in the TCP segment header that is sent by Q to P?

Try it: multiple choice: exactly one correct option

Select one option
Wrong answer costs 1/3 mark in GATE.
Show answer and explanation

Answer: C (official GATE 2021 final answer key)

Concept used: The second handshake segment is SYN+ACK: Q's own initial sequence number, and an acknowledgement of P's SYN, which consumes one sequence number.

First step: Q uses its own number Y as SEQ, and acknowledges the next byte it expects from P, which is X + 1.

Full step-by-step solution

Detailed working, common mistakes and linked mock tests will be available with a free GATEiit account. Log-in is coming soon.

Share this question

WhatsAppDownload image

Source: official GATE 2021 Set 2 CS question paper and final answer key, organised by IIT Bombay. Question paper · Answer key

More Computer Networks PYQs

PracticePractise Computer Networks questions →Full paperAll GATE CSE 2021 Set 2 questions →