Guides to IP addresses, VPNs and online privacy
Clear, practical explanations of how IP addresses, DNS, VPNs and email work, and what they reveal about you. Written for everyone, checked against the official standards.
Common port numbers and what they are used for
A reference list of the most common TCP and UDP port numbers, from 22 SSH and 443 HTTPS to 3389 RDP, with what each one does and which ones to keep closed.
DNS & domains · 2 min readHow to change your DNS server on any device
Step-by-step instructions to change your DNS server to 1.1.1.1, 8.8.8.8 or another resolver on Windows, macOS, iPhone, Android and your router.
DNS & domains · 2 min readHow to find the IP address of a website
Find the IP address behind any website with an online lookup, ping or nslookup, and learn why big sites have many addresses that change by location.
DNS & domains · 2 min readHow to flush your DNS cache (Windows, Mac, Chrome and more)
Clear your DNS cache to fix "site not found" errors and see DNS changes at once. Step-by-step commands for Windows, macOS, Linux, Chrome and phones.
IP basics · 2 min readHow to read and shorten an IPv6 address
IPv6 addresses look intimidating but follow simple rules. Learn the format, how :: shortening works, prefixes like /64, and the address types you will see.
Networking · 2 min readHow to trace the route to an IP address with traceroute
Use traceroute (tracert on Windows) to see every router between you and a server, find where lag or loss starts, and understand the results.
Networking · 2 min readHow to use ping to test your connection
Use the ping command to check whether a server is reachable and how fast your connection responds. Learn to read the results, latency and packet loss.
Security · 2 min readIs public Wi-Fi safe? Risks and how to protect yourself
Free Wi-Fi in cafés, hotels and airports carries real risks, from fake hotspots to snooping. Learn what can go wrong and eight practical ways to stay safe.
DNS & domains · 2 min readPublic DNS servers compared: 1.1.1.1, 8.8.8.8, 9.9.9.9 and more
Addresses, privacy and features of the major public DNS resolvers (Cloudflare, Google, Quad9, OpenDNS) and how to choose one for speed or privacy.
Privacy & VPN · 2 min readWhat does incognito mode actually hide?
Private and incognito browsing stop your device from saving history and cookies. They do not hide your IP or activity from sites, your ISP or employer.
Security · 2 min readWhat is a DDoS attack?
A DDoS attack floods a website, server or home connection with traffic from many sources. Learn the main types, the warning signs and how to stay safe.
IP basics · 2 min readWhat is a dedicated IP address, and do you need one?
A dedicated IP is an address used only by you, for hosting, email or a VPN. How it differs from a shared IP, when it helps and when it is not worth it.
Networking · 2 min readWhat is a default gateway and how do you find it?
The default gateway is the router your device sends internet traffic to. What it does, how to find its IP on Windows, Mac, iPhone and Android, and fixes.
Networking · 2 min readWhat is a MAC address, and how is it different from an IP address?
A MAC address identifies a network card on your local network; an IP address identifies your connection online. The differences, and how to find both.
Networking · 2 min readWhat is DHCP and how does it assign IP addresses?
DHCP automatically gives every device on your network an IP address, gateway and DNS server. Learn how it works, what a lease is and how to fix DHCP problems.
Privacy & VPN · 2 min readWhat is DNS over HTTPS (DoH) and should you turn it on?
DNS over HTTPS encrypts your DNS lookups so your network cannot see which sites you visit. Learn how DoH and DoT work, the trade-offs and how to enable them.
Email · 2 min readWhat is email spoofing and how do you spot it?
Email spoofing fakes the sender address to make phishing look real. Learn how it works, how to check if an email is spoofed and how to protect your own domain.
Privacy & VPN · 2 min readWhat is geo-blocking and why do websites think you are in another country?
Websites use your IP address to block content, change prices or pick a language. How geo-blocking works, why it gets your country wrong and what to do.
Security · 2 min readWhat is HTTPS and what does the padlock mean?
HTTPS encrypts the connection between your browser and a website. What the padlock does and does not prove, how TLS certificates work and what HTTPS hides.
Security · 2 min readWhat is IP allowlisting (whitelisting)?
IP allowlisting lets only approved IP addresses reach a server, admin panel or API. How it works, when it helps and its limits with dynamic IPs and VPNs.
Security · 2 min readWhat is IP spoofing?
IP spoofing forges the source address of network packets. How attackers use it in DDoS attacks, why it cannot be used for browsing and how it is stopped.
Networking · 2 min readWhat is NAT (network address translation)?
NAT lets every device in your home share one public IP address. Learn how it works, the types of NAT, NAT types in gaming and how NAT affects security.
Networking · 2 min readWhat is port forwarding and how do you set it up?
Port forwarding lets devices on the internet reach a server, camera or game console in your home. Learn how it works, how to set it up and how to stay safe.
IP basics · 2 min readWho is my internet service provider (ISP)?
Find out which internet service provider you are using in seconds, why the name may look unfamiliar, and what your ISP can see about your activity.
Networking · 3 min read192.168.1.1, 192.168.0.1 and 10.0.0.1: how to log in to your router
Open your router settings at 192.168.1.1, 192.168.0.1 or 10.0.0.1. Find your router's IP, log in, and fix the most common problems step by step.
DNS & domains · 2 min readDNS record types explained
What A, AAAA, CNAME, MX, NS, TXT, SOA, CAA, PTR and SRV records do, with examples and the most common mistakes to avoid.
IP basics · 2 min readHow accurate is IP geolocation?
IP geolocation is right about the country almost always and the city often, but never the street. Learn how it works and why your location may be wrong.
Privacy & VPN · 2 min readHow to change your IP address
Six ways to change your public or local IP address on any device, from restarting your router to using a VPN, and how to confirm it worked.
IP basics · 2 min readHow to find your IP address on any device
Find your public and local IP address on Windows, macOS, iPhone, Android, Linux and your router, step by step, and learn which one you need.
Privacy & VPN · 2 min readHow to hide your IP address
VPNs, proxies, Tor and mobile networks compared on how much they hide, how fast they are and what they cost.
Email · 3 min readHow to read email headers and trace an email
Email headers show the path a message took, the sender's IP and whether it passed SPF, DKIM and DMARC. Learn to read them and spot phishing step by step.
IP basics · 2 min readIPv4 vs IPv6: what changes for you
Why your device may have two public IP addresses, which one websites see, and whether you need to do anything about it.
Email · 2 min readIs my IP blacklisted? How to check and get delisted
Find out if your IP is on a spam blacklist (DNSBL), why it was listed and how to get it removed, step by step, plus how to stay off blacklists.
IP basics · 2 min readPublic vs private IP address: what is the difference?
Public IP addresses identify you on the internet; private ones work only inside your network. See the private ranges and how NAT connects the two.
Email · 2 min readSPF, DKIM and DMARC explained
SPF, DKIM and DMARC prove an email really comes from the domain it claims. Learn how each works, how to set them up and what pass, fail and softfail mean.
IP basics · 2 min readStatic vs dynamic IP address: which one do you have?
A dynamic IP changes over time, a static IP stays the same. Learn which one you have, when you need a static IP, and what it costs.
Networking · 2 min readSubnet masks and CIDR notation explained
What a subnet mask like 255.255.255.0 means, how CIDR notation like /24 works, how many addresses each size holds, with a cheat sheet and examples.
Privacy & VPN · 2 min readWhat is a DNS leak and how do you prevent it?
A DNS leak reveals the sites you visit to your internet provider even when you use a VPN. Learn why leaks happen and how to fix them on any device.
Privacy & VPN · 2 min readWhat is a proxy server?
A proxy server forwards your requests so websites see its IP instead of yours. The types of proxies, what they are used for and how they differ from a VPN.
Privacy & VPN · 3 min readWhat is a VPN and do you need one?
A VPN encrypts your traffic and hides your IP address from websites. Learn how it works, what it protects, what it does not, and how to choose one.
Privacy & VPN · 2 min readWhat is a WebRTC leak and how do you fix it?
WebRTC can reveal your real IP address to websites even when you use a VPN. Learn why it happens, how to test for it and how to fix it in every browser.
Networking · 2 min readWhat is an ASN (Autonomous System Number)?
An ASN identifies a network that routes its own traffic on the internet, like an ISP or cloud provider. Learn what ASNs are and what yours says about you.
IP basics · 3 min readWhat is an IP address, and what can someone do with yours?
An IP address shows your approximate city and your internet provider. It does not show your name or street address. Here is exactly what it reveals.
Privacy & VPN · 2 min readWhat is browser fingerprinting?
Browser fingerprinting identifies you from your browser's settings and hardware, even without cookies. Learn how it works and how to protect yourself.
Networking · 2 min readWhat is CGNAT (carrier-grade NAT)?
With CGNAT your provider shares one public IPv4 address between many customers. Learn how to tell if you are behind CGNAT and how to work around it.
DNS & domains · 2 min readWhat is DNS and how does it work?
DNS translates names like example.com into IP addresses. Learn how a DNS lookup works step by step, what resolvers and name servers do, and why DNS matters.
Networking · 2 min readWhat is localhost (127.0.0.1)?
Localhost and 127.0.0.1 always point to your own computer. Learn how the loopback address works, what developers use it for, and what ::1 means.
DNS & domains · 2 min readWhat is reverse DNS (PTR record)?
Reverse DNS maps an IP address to a host name with a PTR record. Learn how it works, why mail servers need it, and how to set it up correctly.
Privacy & VPN · 2 min readWhat is Tor and how does it hide your IP?
Tor routes your traffic through three volunteer servers so no one can link you to the sites you visit. How it works, its limits and how it compares to a VPN.
DNS & domains · 2 min readWhat is WHOIS and what can it tell you?
WHOIS shows who registered a domain or IP range, when it expires and who to contact about abuse. Learn what it reveals, why data is hidden, and RDAP.