ITPEC FE Subject A April 2026 Question 24

Topic: NetworksAlso asked in April 2019

In IPv4, which of the following is a description concerning the NAT function of a router that connects some computers to the Internet?

a)It caches the Internet access to speed up the connections when revisiting the same websites.b)It converts between private and global IP addresses.c)It inspects the IP packets during transmission to detect possible attacks and intrusions from the Internet.d)It only passes the IP packets intended for specific terminals.

Explanation

Conversion between private and global IP addresses — NAT translates addresses at the boundary between a private network and the Internet.

Private addresses (the ranges starting 10, 172.16 to 172.31, and 192.168) cannot be routed on the Internet. When a computer inside sends a packet, the router replaces the private source address with its global address and records the mapping; when the reply arrives it restores the private address. NAPT (IP masquerade) also rewrites port numbers, so many computers can share one global address.

Answer (b)

Why not others:

•(a) — caching pages to speed up repeat visits is the job of a proxy server (web cache)
•(c) — inspecting packets to detect attacks and intrusions is an IDS or IPS
•(d) — letting through only the packets meant for specific terminals is packet filtering, a firewall function

Key rule: NAT changes addresses, not content or permissions; caching, inspection and filtering are separate functions even when one box performs them all.

Networks · AI-written, may contain errors

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