問65
頻出度★★★
NAT に関する次の記述中の a, b に入れる字句の適切な組合せはどれか。 NAT は, 職場や家庭の LAN をインターネットへ接続するときによく利用され, [ a ] と [ b ] を相互に変換する。
令和元年度 秋期 ITパスポート試験 問65
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 65
Incorrectア
The private IP address for a is correct, but the ‘MAC address’ for b is wrong. A MAC address is a physical address unique to a network interface (data link layer) and is not what NAT converts. NAT deals with addresses at the IP layer.
- イ
正解 NAT (Network Address Translation) is a technology that mutually converts between a ‘private IP address’, which is valid only inside a LAN, and a ‘global IP address’, which is uniquely valid on the Internet. When connecting a workplace or home LAN to the Internet, the router rewrites packets whose source is an internal device’s private IP address into the router’s global IP address before sending them out, and converts the return packets in the opposite direction. Therefore a = private IP address and b = global IP address, so イ is the correct answer.
Incorrectウ
The ‘host name’ for a is wrong. Mapping a host name to an IP address is the role of DNS, not a function of NAT. The ‘MAC address’ for b is also not something NAT converts, so this option is wrong on two counts.
Incorrectエ
The global IP address for b is correct, but the ‘host name’ for a is wrong. Mapping host names to IP addresses is handled by DNS, whereas NAT is a technology that converts addresses between private IP and global IP.
ここがポイント
- Remember that NAT is a technology that mutually converts between a ‘private IP address’ inside the LAN and a ‘global IP address’ on the Internet side.
- Distinguish the roles of address translation (NAT), DNS which performs name resolution, and the MAC address which is a physical address at the data link layer.
用語