IPA IP 2023 Question 97
A question IPA Japan published in 令和5年度 ITパスポート試験 公開問題 問97, translated into English. ITPEC is based on the same exams.
Which of the following is an appropriate role of a subnet mask?
Explanation
It defines how many leading bits of an IP address are the network address — the subnet mask marks where the network part ends and the host part begins.
A subnet mask is 32 bits written like an IP address: its 1 bits, which run from the beginning, cover the network part, and its 0 bits the host part. With mask 255. (/24), the first 24 bits are the network address, so ANDing 192. with the mask gives the network 192., and 25 is the host. A computer compares network addresses this way to decide whether a destination is on its own network or must be reached through the default gateway.
Answer (b)
Why not others:
- •(a) — finding the MAC address on the LAN from an IP address is ARP
- •(c) — obtaining the TCP/IP settings (IP address, subnet mask, default gateway, DNS server) automatically on connection is DHCP
- •(d) — associating a domain name with an IP address is DNS
Key rule: Match each job to its mechanism: the subnet mask splits network and host parts, ARP finds a MAC address, DHCP hands out settings, DNS resolves names.
Networks · AI-written, may contain errors
This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.