GLOSSARY · 34 TERMS
Glossary of IP, DNS, VPN and proxy terms
Short, careful definitions of the words you meet when you check an IP address, test for leaks or compare proxies. Each entry says what the term means, why it matters, and which free tool lets you see it on your own connection.
Last updated October 29, 2026
The terms are listed alphabetically. For longer explanations, read the guides on VPN vs. proxy and how to fix a DNS leak, or run the full border check.
D
Datacenter proxy
A datacenter proxy runs on a server in a hosting facility, so its IP address belongs to a hosting or cloud company and not to a home or mobile provider.
Read definition →DNS
DNS is the internet's naming system.
Read definition →DNS leak
A DNS leak is when your device sends its DNS lookups to a resolver you did not intend, usually your internet provider's, while you believe a VPN or proxy is handling your traffic.
Read definition →DNS resolver
A DNS resolver is the server that does the lookup work on your behalf.
Read definition →DNSBL
A DNSBL is a list of IP addresses, published through the DNS system, that an operator has marked as sources of spam or abuse.
Read definition →DoH
DNS over HTTPS wraps DNS questions and answers inside ordinary encrypted HTTPS traffic to a resolver, as described in RFC 8484.
Read definition →DoT
DNS over TLS encrypts DNS traffic between your device and a resolver using the same TLS security that protects websites, as set out in RFC 7858.
Read definition →I
IP address
An IP address is a number that identifies a device or network connection on the internet, in the way a street address identifies a building.
Read definition →IPv4
IPv4 is the older and still most common version of the internet's addressing system.
Read definition →IPv6
IPv6 is the newer version of the addressing system, built to replace IPv4.
Read definition →ISP
An ISP is the company that connects you to the internet, whether through a cable, fibre, DSL, fixed wireless or mobile network.
Read definition →P
Port
A port is a number from 0 to 65535 that tells a computer which program should receive incoming network data.
Read definition →Proxy
A proxy server is an intermediary that makes requests on your behalf.
Read definition →Public vs. private IP address
A public IP address is reachable across the internet and is the one websites see.
Read definition →R
Residential proxy
A residential proxy sends your traffic through an IP address that a home internet provider assigned to a household.
Read definition →Reverse DNS
Reverse DNS turns an IP address back into a name, the opposite of a normal lookup.
Read definition →Rotating proxy
A rotating proxy gives you a different IP address from a pool, either on every request or at set intervals, while you keep using the same connection details.
Read definition →S
SOCKS5
SOCKS5 is a proxy protocol, specified in RFC 1928, that relays network connections at a lower level than HTTP.
Read definition →Split tunneling
Split tunneling lets you decide which apps, sites or destinations go through the VPN tunnel and which use your normal internet connection.
Read definition →Sticky session
A sticky session is a proxy setting that keeps you on the same exit IP address for a set period, or until you end the session, instead of changing it with each request.
Read definition →STUN
STUN is a simple protocol where a device asks a public server, "what address and port do you see me coming from?" The server replies with the answer.
Read definition →Subnet and CIDR
A subnet is a block of consecutive IP addresses treated as one network.
Read definition →