ITPEC FE Morning October 2020 Question 44

Packet-Filtering Firewall Rules — configure firewall to allow HTTP access from internal PCs to an external web server.

When a PC accesses a web server on port 80:

• •Request (PC → Web server): source port = 1024+ (ephemeral), destination port = 80
• •Response (Web server → PC): source port = 80, destination port = 1024+ (same ephemeral port)

Why not others:
- (a) — both rules show source port 80; the client never uses port 80 as its source
- (b) — the server's response incorrectly shows source 1024+ and destination 80 (reversed)
- (d) — the server's response targets destination port 80 on the PC, but the PC listens on an ephemeral port (1024+)

Key rule: The client always picks a random ephemeral port (1024+) as source; the server listens on a well-known port (80). The response packet mirrors the request — source and destination swap.

AI-generated — may contain errors