問65
頻出度★★★
IPアドレスに関する記述のうち，適切なものはどれか。
平成21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
A notation such as 192.168.1.1 is an IPv4 address, which is 4 bytes = 32 bits long. The total number of addresses that can be represented is 2 to the 32nd power = about 4.3 billion, which is fewer than the world's population (about 7 billion). This shortage is the IPv4 address exhaustion problem, and it is also the reason 128-bit IPv6 was introduced.
Incorrectイ
IP addresses are not managed by the governments of each country. Globally they are overseen by ICANN/IANA, and they are allocated hierarchically through the regional RIRs (APNIC for the Asia-Pacific region), then national NIRs (JPNIC in Japan) and ISPs. It is an international management system run mainly by private-sector bodies.
Incorrectウ
A global IP address must be unique across the entire Internet. If the only requirement were that addresses not overlap within each country, the destination could not be identified in communication that crosses national borders, and packets could not be delivered correctly. Uniqueness is required worldwide, not per country.
- エ
正解 エ is correct. IP addresses are divided into “global IP addresses,” which must be unique across the entire Internet, and “private IP addresses,” which are only for use inside an organization (a local network). The ranges 10.0.0.0-10.255.255.255, 172.16.0.0-172.31.255.255, and 192.168.0.0-192.168.255.255 are reserved as private IP addresses, and addresses in these ranges are not forwarded on the Internet. Therefore, within a local network such as inside the same company, there is no problem even if the addresses overlap with those of another organization, and the administrator may assign them freely. When traffic goes out to the Internet, it is translated into a global IP address by NAT or NAPT (IP masquerade).
ここがポイント
- A global IP address must be unique across the entire Internet, and it is allocated hierarchically by RIRs, NIRs, and ISPs under ICANN/IANA at the top. It is not managed by governments.
- Private IP addresses (10/8, 172.16/12, 192.168/16) are for use only inside an organization; they may overlap between organizations and can be assigned freely. When communicating with the outside, they are translated by NAT or NAPT.
- An IPv4 address is 32 bits, giving a total of about 4.3 billion addresses. That is fewer than the world's population, which led to address exhaustion, so 128-bit IPv6 was prepared.
用語