ITPEC FE Morning October 2021 Question 31
Which of the following is a mechanism that enables multiple terminals to have private addresses different from each other to connect to the Internet by sharing a single global IP address?
Explanation
NAPT — it translates private address and port pairs to one global address with different port numbers.
When a terminal sends a packet to the Internet, the NAPT router replaces its private IP address and source port with the global IP address and a port number it assigns, and records the pair in a table. Replies come back to that port, so the router knows which terminal to return them to. Plain NAT translates addresses only, so one global address serves one terminal at a time; adding the port lets many share it.
Answer (c)
Why not others:
- •(a) DHCP — hands out IP addresses and other settings to terminals; it does not translate addresses
- •(b) DNS — resolves domain names to IP addresses
- •(d) RADIUS — a protocol for authenticating users and authorising network access
Key rule: NAT maps addresses one to one; NAPT (also called IP masquerade or PAT) adds port numbers so many private addresses share one global address.
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