問73
頻出度★★★
インターネットのドメイン名と IP アドレスを対応付ける仕組みはどれか。
平成24年度 春期 ITパスポート試験 問73
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 73
- ア
正解 The correct answer is ア (DNS). DNS stands for Domain Name System. It is the mechanism that maps domain names on the Internet (for example, www.example.co.jp) to IP addresses (for example, 192.0.2.1) and converts between the two. This conversion process is called name resolution. People specify what they want to reach by using a domain name, which is an easy-to-remember string, but what actually indicates the other party in real communication is the IP address, so a mechanism is needed to bridge the gap between them. When a URL is entered into a browser, the user's PC first queries a DNS server, receives the corresponding IP address, and only then starts the actual communication with that IP address. Another characteristic of DNS is that its management information is held hierarchically, distributed among DNS servers all over the world, and the target information is obtained by following the higher-level servers in turn.
Incorrectイ
FTP (File Transfer Protocol) is a protocol for exchanging files between computers over a network. It is used for purposes such as uploading website content to a server, but what it handles is the transfer of files; it does not map domain names to IP addresses. On the contrary, when a server name is specified for an FTP connection, it is DNS that plays the role of converting that name into an IP address.
Incorrectウ
SMTP (Simple Mail Transfer Protocol) is a protocol for sending email and for relaying mail between mail servers. There are situations where the destination mail server is looked up from the domain name on the right-hand side of a mail address, but the name resolution itself is again performed by DNS; SMTP stays limited to the role of carrying the mail. It is not a mechanism that manages a table matching names to addresses.
Incorrectエ
The Web (WWW: World Wide Web) is a mechanism for providing information that links documents all over the world to one another through hypertext so that they can be viewed in a browser. Because the domain name in a URL is used when browsing, the Web is on the side that uses DNS, but the Web itself does not map names to addresses. It tends to be chosen because domain names are seen with it so often, but that is a confusion of roles.
ここがポイント
- DNS (Domain Name System) is the mechanism that maps domain names and IP addresses to each other, and this conversion is called name resolution. Grasp the division of roles: a domain name is a notation that makes things easy for people to handle, while an IP address is a number that communication equipment uses to identify the other party.
- Memorize frequently tested protocols together with their roles: DNS for name resolution, FTP for file transfer, SMTP for sending and relaying mail, POP3 and IMAP for receiving mail, HTTP for transferring web pages, and DHCP for automatically assigning IP addresses. What gets tested is that the jobs they are in charge of differ even when the names look similar.
用語