IP Glossary
Plain-language definitions of IP and networking terms.
- IPアドレス / IP address
- A number that identifies a device on a network. IPv4 is 32-bit (e.g. 192.0.2.1); IPv6 is 128-bit.
- IPv4
- The 32-bit IP addressing scheme with about 4.3 billion addresses, written in dotted decimal.
- IPv6
- The 128-bit IP addressing scheme designed to overcome IPv4 exhaustion, written in colon-separated hex.
- CIDR （サイダー）
- Classless Inter-Domain Routing — notation like /24 that expresses a network range by prefix length.
- サブネットマスク / Subnet mask
- A 32-bit mask separating the network and host portions of an address (e.g. 255.255.255.0).
- グローバルIP / Public IP
- A globally unique IP address reachable from the public Internet.
- プライベートIP / Private IP
- Addresses for internal use (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), reaching outside via NAT.
- NAT
- Network Address Translation — maps private to public IPs so many devices share one public address.
- DNS
- Domain Name System — the distributed database that maps domain names to IP addresses.
- 逆引き / Reverse DNS (PTR)
- Resolving a host name from an IP address, using PTR records.
- WHOIS
- A protocol/service to query registration data of domains and IPs, now moving to RDAP.
- RDAP
- Registration Data Access Protocol — the successor to WHOIS returning JSON over HTTP. Used by this site.
- RIR
- Regional Internet Registry — bodies that manage IP allocation per region (APNIC/ARIN/RIPE/LACNIC/AFRINIC).
- ASN
- Autonomous System Number — identifier for an autonomous system in BGP routing.
- MACアドレス / MAC address
- A 48-bit hardware address unique to a network interface; the first 24 bits are the vendor OUI.
- ループバック / Loopback
- A special address pointing to the host itself: 127.0.0.0/8 (127.0.0.1) in IPv4, ::1 in IPv6.
- DHCP
- A protocol that automatically assigns IP addresses and other network settings.