Essential technical definitions covering internet routing, IP subnetting, DNS architecture, and network security protocols.
A numerical label assigned to each device connected to a computer network.
An Internet Protocol (IP) address serves two primary functions: host or network interface identification and location addressing. Version 4 (IPv4) defines a 32-bit number, while Version 6 (IPv6) defines a 128-bit address space.
Fourth revision of IP using 32-bit addresses formatted as four decimal octets.
Internet Protocol Version 4 allocates roughly 4.29 billion unique addresses. Exhaustion of unallocated IPv4 address pools led to the rapid development and deployment of IPv6 and widespread NAT adoption.
Latest version of IP utilizing 128-bit hexadecimal addressing to provide 340 undecillion addresses.
IPv6 solves IPv4 address exhaustion, eliminates standard NAT requirements, simplifies packet headers for more efficient router handling, and supports mandatory IPsec support and stateless auto-configuration (SLAAC).
A globally unique 16-bit or 32-bit identifier for a connected group of IP networks.
Autonomous Systems (AS) are operated by one or more network operators (such as ISPs, universities, or tech enterprises) with a single, clearly defined routing policy presented to the global internet via BGP.
A method for allocating IP addresses and IP routing without legacy address classes.
CIDR notation uses a slash followed by the count of leading continuous network bits (e.g., 192.168.1.0/24), drastically reducing the size of global internet routing tables.
Resolution of an IP address back to its associated domain name using a PTR record.
Unlike standard forward DNS (name to IP), reverse DNS maps an IP to a hostname using the special domains `in-addr.arpa` for IPv4 and `ip6.arpa` for IPv6.
A DNS record type used exclusively for reverse DNS queries.
PTR records provide the authoritative domain name attached to an IP address, heavily relied upon by anti-spam email filters to verify sending mail server legitimacy.
The standardized exterior gateway protocol designed to route data between Autonomous Systems.
BGP makes routing decisions based on paths, network policies, or rule-sets configured by system administrators, making it the foundational routing adhesive of the World Wide Web.
An organization that provides services for accessing, using, or participating in the Internet.
ISPs may be organized in various forms, such as commercial, community-owned, non-profit, or privately owned, operating upstream transit, peering agreements, and customer last-mile connections.
A technique of remapping an IP address space into another by modifying network traffic headers.
NAT enables multiple private devices in a local area network (LAN) to share a single public IPv4 address, mitigating IPv4 exhaustion at the cost of end-to-end connectivity simplicity.
Large-scale network address translation implemented at the telecom or ISP infrastructure tier.
Also known as Large-Scale NAT (LSN), CGNAT allows an internet provider to assign private addresses (such as RFC 6598 100.64.0.0/10) to residential subscribers, routing hundreds of customers via a single shared public IPv4.
The modern, JSON-based successor to WHOIS for querying domain and IP registration data.
Specified by the IETF (RFC 7480-7484), RDAP provides structured, RESTful responses, internationalization support, standardized error codes, and secure authenticated access tiers unlike legacy port 43 WHOIS.
A legacy query and response protocol used for querying databases that store registered users of an IP or domain.
WHOIS delivers unstructured plain-text records regarding IP subnet allocations, administrative contacts, technical abuse desks, and creation/expiration timestamps.
The estimation of the real-world geographic location of an internet-connected device.
Geolocation databases aggregate BGP routing tables, latency triangulation, ISP registry declarations, and user-submitted data to determine country, region, city, and approximate coordinates.
The hierarchical naming system for computers and resources connected to the Internet.
DNS translates human-readable hostnames (such as ip-address-lookup.com) into numerical IP addresses necessary for locating and routing computer services worldwide.
A protocol for performing remote DNS resolution via encrypted HTTPS.
DoH prevents eavesdropping and tampering of DNS data by man-in-the-middle attackers by encrypting data between the DoH client and the DoH-based DNS resolver.
A network addressing and routing methodology whereby a single IP is shared by multiple physical servers.
Routers direct incoming packets to the nearest operational server node according to BGP routing metrics, offering high availability, low latency, and DDoS attack mitigation (common in CDNs and public DNS like 8.8.8.8 and 1.1.1.1).
One-to-one transmission from one point in the network to another specific singular recipient.
The vast majority of typical web browsing and client-server interactions are unicast transmissions, contrasting with multicast and anycast.
An unallocated, reserved, or private IP address that should never appear in public routing tables.
Bogon filtering protects networks against packet spoofing and misconfigurations by dropping packets advertising unassigned IP prefixes or reserved ranges like 10.0.0.0/8 or 127.0.0.0/8 on public border routers.
A special IP address used by a host to route network communications back to itself.
IPv4 reserves the entire 127.0.0.0/8 block (commonly 127.0.0.1) and IPv6 reserves ::1 for loopback interfaces, ensuring local diagnostic testing never hits a physical network adapter.
A network management protocol used to automatically assign IP addresses and network parameters.
DHCP dynamically leases IP addresses, default gateways, subnet masks, and DNS servers to client devices joining a local network.
An encrypted tunnel connecting a client device to a remote server, masking the true client IP.
VPNs encapsulate and encrypt client network packets. Websites observe the remote VPN exit node's public IP rather than the user's local residential ISP assignment.
A 32-bit number that separates the network address and the host address portions of an IP.
A subnet mask such as 255.255.255.0 designates that the first 24 bits belong to the network prefix and the remaining 8 bits designate individual local host machines.
A unique hardware identifier assigned to a network interface controller for local communications.
Unlike IP addresses which operate at Layer 3 (Network Layer) and change across networks, MAC addresses operate at Layer 2 (Data Link Layer) and are not broadcast across the global internet.
A mechanism that limits the lifespan or lifetime of data or packets in a computer network.
In IP packet headers, TTL prevents packets from circulating indefinitely inside routing loops. In DNS, TTL specifies how long a DNS resolver may cache a record before re-querying.