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IP addresses, DNS and networking, explained
Original guides that answer one question completely, with the sources behind each one and a tool to try the idea on your own connection.
Start here
The five pieces most people need first.
- 01 · FundamentalsWhat is an IP address?An IP address is the label that lets devices find each other on a network. What one looks like, who assigns it, and what it can and cannot reveal about you.
- 02 · Addressing and routingPublic vs private IP addressesYour devices have a private address from your router and share one public address with the internet. The ranges, how NAT links them, and how to tell which is which.
- 03 · Addressing and routingIPv4 vs IPv6: what changedIPv4 has 4.3 billion addresses and IPv6 has 340 undecillion. How the two differ, how to read IPv6 notation, why both are in use, and what it means for your privacy.
- 04 · FundamentalsHow to find your IP address on any deviceStep-by-step ways to find your public and private IP address on Windows, macOS, Linux, Android, iPhone and your router, with the terminal commands for each.
- 05 · FundamentalsThe complete guide to IP addressesOne reference for the whole subject: how addresses are built, the reserved ranges you will meet, how they are allocated and routed, and how to read a lookup result.
All guides
Fundamentals
What an IP address is, how to find yours, and the map of the whole subject.
Addressing and routing
IPv4, IPv6, private ranges, NAT, subnets and the networks that carry your traffic.
DNS
How names become addresses, and how addresses map back to names.
Privacy
What a website can see when you connect, and where it comes from.
Tools that go with the guides
Every guide leads into something you can run.
- Check your public IP addressSee the address every website sees, with the network and location behind it.
- Look up any IP address, domain or URLOwner, network, location estimate and risk flags for whatever you paste in.
- Run a DNS lookupA, AAAA, MX, TXT, NS and more for a name, or the name behind an address.
- Test for IP, DNS and WebRTC leaksFind out whether a VPN is really hiding what you think it is.
- Check whether an address is a VPN, proxy or Tor exitSee how a site would classify the network you are on.
- See the headers your browser sendsEvery request header, explained in plain language.
- View your browser fingerprintWhat a site can learn about your device without a cookie.
- Check an address against blocklistsLive results from dozens of DNS blocklists, with delisting links.
- Calculate a subnetNetwork, broadcast, mask, host range and binary form for any IPv4 or IPv6 prefix.