問58
頻出度★★☆
PCがネットワークに接続されたときにIP アドレスを自動的に取得するために使用されるプロトコルはどれか。
平成26年度 春期 ITパスポート試験 問58
テクノロジ系ネットワーク › 通信プロトコル
This question's explanation and your answers so far.
解説
問 58
- ア
正解 The correct answer is ア, DHCP. DHCP (Dynamic Host Configuration Protocol) is a protocol that automatically assigns the settings needed for communication, starting with an IP address, to a device that connects to a network. A DHCP server is provided on the network, and a PC (the DHCP client) broadcasts a request for its settings when it starts up or connects to the network. From the range of addresses it manages in advance (the address pool), the DHCP server picks one unused IP address and lends it to the client together with the subnet mask, the default gateway, the address of the DNS server, and so on. The loan has an expiration time (the lease period), and an address whose lease has expired is reclaimed and reused. Thanks to this mechanism, users no longer have to set an IP address by hand on each machine, which prevents configuration mistakes and accidents in which the same address is assigned twice. It is especially useful for devices that move across networks, such as laptop PCs and smartphones, and in environments where the number of connected devices changes, such as a company LAN or a public wireless LAN.
Incorrectイ
HTTP (HyperText Transfer Protocol) is a protocol for exchanging content such as HTML files and images between a web browser and a web server. It is used for browsing web pages and plays no part in assigning IP addresses. On the contrary, communicating over HTTP requires that the PC already has an IP address configured.
Incorrectウ
NTP (Network Time Protocol) is a protocol for obtaining accurate time information from a time server over the network and adjusting a device's internal clock (time synchronization). It is important for purposes such as aligning the timestamps in logs, but what it handles is time, not IP addresses. The phrase “obtain automatically” sounds similar, but what is obtained is different.
Incorrectエ
SMTP (Simple Mail Transfer Protocol) is a protocol for sending e-mail and for relaying it between mail servers. Note that what is used on the receiving side is POP3 or IMAP4. All of these relate to delivering mail, and have nothing to do with automatically obtaining an IP address when connecting to a network.
ここがポイント
- DHCP is the protocol that automatically assigns an IP address, subnet mask, default gateway, DNS server address, and so on to a device that connects to a network. Addresses are lent out with a lease period, which saves the trouble of manual configuration and prevents duplicate addresses.
- The IT Passport exam often asks you to match the main protocols with their roles. It is a good idea to memorize them together with their uses: DHCP = automatic assignment of IP addresses, HTTP = web browsing, NTP = time synchronization, SMTP = sending mail (receiving is POP3 / IMAP4), DNS = mapping between domain names and IP addresses, FTP = file transfer.
用語