ITPEC FE Morning April 2023 Question 44
ITPEC FE Morning April 2023 — Question 44 of 80
Packet Filtering Firewall Rules — select correct source/destination port combination for HTTP access.
A PC on an internal network accesses a web server (port 80) through a packet filtering firewall. Two rules are needed:
Outbound (PC → Web server):
- Source port: 1024 or higher (ephemeral, assigned by OS)
- Destination port: 80 (web server listens here)
Inbound (Web server → PC):
- Source port: 80 (server responds from its listening port)
- Destination port: 1024 or higher (back to client's ephemeral port)
Why not others:
- (a) — PC source port is 80 outbound — incorrect, clients use ephemeral ports
- (b) — PC source port is 80 outbound — same error as (a)
- (d) — server reply destination port is 80 — server replies to the client's ephemeral port, not 80
Key rule: Clients always use an ephemeral port (≥1024) as source; servers listen on well-known ports (80 for HTTP). The return packet mirrors this.
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