ITPEC FE Morning April 2018 Question 35
ITPEC FE Morning April 2018 — Question 35 of 80
TCP Port Numbers in HTTP Response — response packet mirrors source/destination ports of the request.
Given a request packet from PC to web server:
- Request: source = 50001 (ephemeral), destination = 80 (HTTP)
- Response: source = 80, destination = 50001
The response simply swaps the source and destination ports from the request.
Why not others:
- (b) 50001 → 80 — this repeats the request direction, not the response
- (c) random → 80 — the server uses its well-known port 80, not a random one
- (d) random → 50001 — the server responds from port 80, not a new port
Key rule: In TCP, the response packet reverses the source/destination port pair of the request. The server always responds from its well-known port to the client's ephemeral port.
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