Definitions

WhenIP Glossary

Plain-English definitions for the networking terms you see across WhenIP Academy, tool modals, console results, and the debug / issue panel.

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How to use this page

Use the glossary as a quick field guide when a tool result mentions something unfamiliar. The definitions stay short on purpose so you can get oriented fast and then jump into a deeper guide when you want the full story.

Start with IP and Addressing if you are new to public vs private IPs.
Use DNS and Names when you see terms like A, AAAA, PTR, CNAME, or MX.
Use Diagnostics and Routing for ping, traceroute, latency, packet loss, CIDR, and subnets.
Use Probe Locations and Vantage Points when the same test changes between regions.
Use Privacy and Traffic Path for VPN, proxy, NAT, WebRTC, and browser relay behavior.

Best paired with the live tools

When a result looks strange, compare the glossary definition with the Academy guide linked nearby. That makes the tool output much easier to interpret without guessing, especially when the result changes between probe locations.

IPv4 vs IPv6Understand why one family may appear while the other is missing. Ports and filteringUnderstand what open, closed, and filtered really mean.Probe location differencesLearn why routing and policy can change results by region.

Need a quick operational view instead? The FAQ gives short answers, while the Academy gives deeper explainers.

Core Basics

IP and Addressing

The terms below explain the basics of how addresses are identified, assigned, and described on a network.

IP address: A network identifier used so devices and services can exchange traffic across a network path.
Public IP address: The routable address websites and internet services see when your traffic exits to the public internet.
Private IP address: An address used only inside a local network, such as 192.168.1.10, and not directly routed on the public internet.
IPv4: The older 32-bit IP format, such as 203.0.113.10, still used by most consumer networks today.
IPv6: The newer 128-bit IP format designed to solve address exhaustion and improve long-term internet scaling.
ASN: An Autonomous System Number that identifies a network operator, carrier, or large routing domain on the internet.
ISP: Internet Service Provider, the company carrying your traffic from your connection out to the internet.
Geolocation: An estimated physical location based on IP intelligence. It is usually useful for country or city-area detection, not exact street-level certainty.

Names and DNS

DNS and Hostnames

These definitions help when you run DNS or reverse DNS lookups and need to understand the record types returned.

DNS: The Domain Name System that maps hostnames like example.com to IP addresses and other service data.
rDNS: Reverse DNS, a PTR-based lookup that maps an IP address back to a hostname.
PTR record: A DNS record used for reverse lookups from IP address to hostname.
A record: A DNS record that maps a hostname to an IPv4 address.
AAAA record: A DNS record that maps a hostname to an IPv6 address.
CNAME: A DNS alias that points one hostname at another hostname instead of directly to an IP.
MX record: A DNS record listing the mail servers responsible for receiving mail for a domain.
TXT record: A text-bearing DNS record often used for SPF, DKIM, DMARC, verification strings, and service metadata.
NS record: A DNS record that lists the authoritative nameservers for a zone.
Authoritative DNS: The DNS server responsible for the final, official answer about a zone.
Recursive resolver: The DNS server that follows the lookup path on behalf of a client and returns the final result.
WHOIS: A registration lookup that can show registrar, dates, or ownership metadata for a domain, though privacy rules often limit detail.

Diagnostics

Ports, Reachability, and Routing

These are the terms that appear most often when you run port checks, pings, traceroutes, or subnet calculations.

Port: A logical service number used to identify a listening application, such as 80 for HTTP or 443 for HTTPS.
Open port: A port with a listening service that accepted the connection attempt.
Closed port: A port that actively rejected the connection because nothing is listening there or the host refused it.
Filtered port: A port that did not give a clear answer before timeout, often because of a firewall, ACL, NAT boundary, or upstream policy.
Ping: A reachability test that usually uses ICMP echo requests and replies to measure if a target answers and how quickly.
Traceroute: A path discovery tool that reveals the routers or hops between one network and another.
Hop: One router or forwarding step along a traceroute path.
Latency: The delay between sending a request and receiving a response, usually measured in milliseconds.
Packet loss: Traffic that never arrives or is discarded somewhere along the path.
CIDR: Classless Inter-Domain Routing notation such as /24 or /64 that expresses how much of an address identifies the network.
Subnet mask: The IPv4 mask that separates the network portion of an address from the host portion.
Gateway: The next-hop router that forwards traffic off your local network toward its destination.

Global Comparison

Probe Locations and Vantage Points

These terms help when the same test gives a different answer from San Francisco, New York, Amsterdam, or future WhenIP probe locations.

Probe: A WhenIP server that runs diagnostics such as ping, traceroute, or port checks from its own network location.
Probe location: The city or region where a WhenIP probe runs, such as San Francisco or Amsterdam.
Vantage point: The network location from which a test is observed or executed. Different vantage points can see different routes and policies.
Egress: The point where traffic leaves a network and becomes visible to the public internet from that path.
Anycast: A routing method where the same service IP can be announced from many places, often steering users to different nearby nodes.
Route asymmetry: A condition where the path out and the path back are different, which can make latency or hop patterns look uneven.
Regional policy: Filtering, CDN behavior, DNS answers, or security rules that differ depending on which location reaches the service.

Privacy and Traffic Path

How your path can change

These terms explain why the IP address or route websites see may differ from what you expect on a local device.

NAT: Network Address Translation, commonly used to share one public IP across many private devices.
VPN: A virtual private network that routes traffic through another network path, often changing the public IP websites see.
Proxy: An intermediary service that makes network requests on your behalf and can change the apparent source address.
Browser privacy relay: A browser or platform feature that relays or masks your public IP to reduce direct exposure to websites.
Header: Metadata sent with an HTTP request or response, such as host, user-agent, or forwarding information.
User-Agent: A header that identifies the browser, app, or device making the request.
WebRTC: A browser technology for real-time communication that may reveal local or public connection candidates.
ICE candidate: A possible network path gathered by WebRTC during connection setup.