IP, networking & BGP terms explained
Plain-English explanations of the concepts behind every WorldIP.io lookup — what each term means, what it looks like, and how it shapes the way the Internet routes traffic.
What is an IP address?
An IP address is a unique numeric identifier assigned to every device on a network. Learn how IPv4 addresses work, what they look like, and how they route Internet traffic.
What is CIDR?
CIDR (Classless Inter-Domain Routing) is a way to represent IP address ranges using a network/prefix-length notation like 192.0.2.0/24. Learn how CIDR replaced classful addressing and enables modern Internet routing.
What is an ASN?
An ASN (Autonomous System Number) is a unique identifier for networks that announce routes on the Internet via BGP. Examples: Google is AS15169, Cloudflare is AS13335.
What is IPv4?
IPv4 is the fourth version of the Internet Protocol, using 32-bit addresses. With ~4.3 billion total addresses, the IPv4 pool was formally exhausted at the top level in 2011.
What is IPv6?
IPv6 is the successor to IPv4, using 128-bit addresses (340 undecillion unique). Designed in the 1990s to solve IPv4 exhaustion, it's been deployed alongside IPv4 since the 2000s.
What is reverse DNS?
Reverse DNS (rDNS) maps an IP address back to a hostname — the opposite of normal DNS. Implemented via PTR records in the .in-addr.arpa zone.
What is WHOIS?
WHOIS is a protocol for querying databases about domain and IP address ownership. Learn what WHOIS data reveals, how to look it up, and its role in abuse reporting.
What is BGP?
BGP (Border Gateway Protocol) is the routing protocol that glues the Internet together. ASNs announce IP prefixes via BGP so every router knows how to reach them.
What is a subnet mask?
A subnet mask defines which portion of an IP address is the network and which is the host. Older notation for CIDR prefix length.
