問74
頻出度★★★
インターネットからの不正アクセスを防ぐことを目的として, インターネットと内部ネットワークの間に設置する仕組みはどれか。
平成21年度 春期 ITパスポート試験 問74
This question's explanation and your answers so far.
解説
問 74
Incorrectア
A DNS server is a server for name resolution: it maps domain names such as www.example.co.jp to IP addresses and vice versa, and it is a mechanism that makes communication possible. It has no function for judging whether access should be allowed and blocking unauthorized access, so it is incorrect.
Incorrectイ
WAN (Wide Area Network) refers to the wide-area network itself, which links the LANs of remote sites by means such as carrier lines; it is a term that indicates a type of network. It is not a defensive mechanism installed at a boundary, so it is incorrect.
- ウ
正解 The correct answer is “ウ Firewall.” A firewall is a mechanism installed at the boundary between an external network such as the Internet and an internal network such as a company LAN. It inspects the packets that pass through it using conditions such as source/destination IP address, port number, and protocol, allowing only permitted communication through and blocking everything else. Only a firewall satisfies both the installation position stated in the question (installed between the Internet and the internal network) and its purpose (preventing unauthorized access from the Internet), so ウ is the correct answer.
Incorrectエ
A router is a relay device that connects networks and forwards packets along the best route by looking at the destination IP address. Its installation position can indeed be a boundary, but its original role is route control (routing); it is not a mechanism whose purpose is to prevent unauthorized access, so it is incorrect. (In actual products a router sometimes also has firewall functions built in, but since this question asks about purpose, ウ is the appropriate answer.)
ここがポイント
- Definition of a firewall: a security mechanism installed at the boundary between the Internet and an internal network that inspects communication, lets only permitted communication pass, and blocks unauthorized access from outside.
- Telling the roles of network terms apart: DNS server = name resolution, WAN = the classification “wide-area network,” router = route control (routing), firewall = communication control (defense) at the boundary. When the purpose is to prevent something, the answer is a firewall.
用語