問57
頻出度★★★
通信事業者が構築したネットワークを利用し, インターネットで用いられているのと同じネットワークプロトコルによって, 契約者の拠点間だけを専用線のようにセキュリティを確保して接続する WAN サービスはどれか。
平成28年度 秋期 ITパスポート試験 問57
This question's explanation and your answers so far.
解説
問 57
Incorrectア
DHCP is a protocol that automatically assigns configuration information such as an IP address, subnet mask, and default gateway to terminals connecting to a network. It is a mechanism for distributing addresses, not a WAN service that connects sites, so it is wrong.
- イ
正解 The correct answer is イ, “IP-VPN”. IP-VPN is a WAN service that uses a closed IP network built by a telecommunications carrier itself (a network isolated from the Internet) and, using the same IP protocol as the Internet, connects only between a subscriber's sites. Because routing takes place inside the carrier's closed network, it can provide a secure site-to-site connection isolated from third parties, just like a dedicated line, at a lower cost than a dedicated line. It matches all the conditions in the question: a network built by a telecommunications carrier, the same protocol as the Internet (i.e., IP), and securing the connection only between sites like a dedicated line.
Incorrectウ
ISDN is a legacy communication service that digitizes telephone lines to handle voice and data in an integrated way. It is a public network using circuit-switching / packet-switching, which differs from IP-VPN that securely connects sites over a closed network based on the IP protocol, so it is wrong.
Incorrectエ
VLAN is a technology that logically divides a single switch (LAN) into multiple networks; its scope is the local LAN. It is not a WAN service that connects distant sites using a telecommunications carrier's network, so it is wrong.
ここがポイント
- IP-VPN = a WAN service that uses a telecommunications carrier's closed IP network and, with the IP protocol, connects a subscriber's sites securely like a dedicated line.
- Distinguishing the confusing terms: DHCP is automatic address assignment, ISDN is a digital public line, and VLAN is logical division of a LAN — none of them is a site-to-site WAN service.
用語