問59
頻出度★★★
DNS の説明として, 適切なものはどれか。
平成21年度 春期 ITパスポート試験 問59
テクノロジ系ネットワーク › ネットワーク応用
This question's explanation and your answers so far.
解説
問 59
Incorrectア
“A system for performing various information searches on the Internet” is a description of a search engine. A search engine uses crawlers to collect and index web pages and then finds the relevant pages from keywords; both its purpose and its mechanism differ from those of DNS, which maps names to IP addresses.
- イ
正解 The correct answer is イ. DNS (Domain Name System) is a system that maps the host names (domain names) given to devices connected to the Internet to the IP addresses actually used in communication. For people, a string such as www.example.co.jp is easier to remember, but communication between computers needs the numeric IP address. DNS servers therefore hold, in a distributed way, tables saying “this name corresponds to this IP address,” and convert them in response to queries. This conversion process is called name resolution. When you enter a URL in a browser, it first queries DNS to obtain the other side's IP address, and only then does the connection begin. The statement in イ, that it is a system that maps the host names of devices connected to the Internet to their IP addresses, expresses exactly this role, so it is appropriate.
Incorrectウ
“A personal authentication system for shopping online safely” describes security mechanisms such as a certificate authority (CA) that issues digital certificates, SSL/TLS, and identity verification services. DNS only handles name resolution; it has no function for confirming that a user is the person they claim to be, or for encrypting the content of communication.
Incorrectエ
“A system that manages individual e-mail addresses for delivering mail” is the role of mail servers (SMTP servers and POP servers) or of a directory service. DNS does use MX records to indicate which mail server should receive mail addressed to a given domain, but what it manages is only the correspondence between host names and IP addresses, not the individual e-mail addresses themselves.
ここがポイント
- DNS = Domain Name System. It is a distributed system that maps host names (domain names) and IP addresses to each other and performs name resolution. When you access a site by URL, a DNS server is queried first to obtain the IP address, and only then does communication begin.
- Tell confusing Internet terms apart by their roles: information search = search engine; identity verification and encryption = certificate authority / digital certificates and SSL/TLS; sending and receiving mail = SMTP and POP mail servers; mapping names to IP addresses = DNS.
用語