Network and DNS guides
Plain-language answers to the questions behind our tools. Each guide explains one topic, shows real commands and records, and links to the tool that checks it on your own domain or connection.
DNS
- What is DNS?How a name becomes an address, step by step.
- How long does DNS propagation take?Typical times, why they vary and how to speed it up.
- What is DNS TTL?What it controls, typical values and a safe change plan.
- DNS record types explainedEvery common record type, what it does and an example.
- Reverse DNS lookupPTR records, command-line checks and mail servers.
- DNS lookup from the command linenslookup, dig and PowerShell, with examples.
- What is DNS cache and how to flush itWhere DNS is cached and the commands to clear it.
- DoH vs DoTTwo ways to encrypt DNS, and which one to pick.
- DNS attacksSix ways DNS gets abused, and the fix for each.
Domain
- When does a domain expire?Find the expiry date and what happens after it.
- WHOIS vs RDAPThe registration lookup you know, and its modern replacement.
IP and network
- IPv4 vs IPv6Address size, NAT, setup and speed compared.
- How to test IPv6Check IPv6 in a browser or from the command line.
- Port forwarding explainedHow it works, how to set it up and why it fails.
- How to check open portsList listening ports and test them from outside.
- How to find your IP addressPublic, private and router addresses on every device.
- How accurate is IP geolocation?What the location is based on and why it can be wrong.
- IPv6 address format and examplesEight groups, the :: shortcut and special prefixes.
- Subnetting cheat sheetCIDR, masks and host counts in one table.
- SSH port forwarding explainedLocal, remote and dynamic tunnels with commands.
- Identify a MAC addressRead a MAC address and find out who made the device.
- Remove an IP from a blacklistFind the listings, fix the cause, ask to be removed.
Email authentication
- SPF, DKIM and DMARC explainedWhat each record checks and how they fit together.
- SPF record syntaxEvery mechanism, the lookup limit and examples.
- DMARC policies explainedTags, alignment and moving from none to reject.
- What is a DKIM selector?Find your selector in a header and read the record.
- How to read a DMARC reportTurn on rua reports and read the XML.
- Why DKIM or DMARC failsRead the failure, find the cause, apply the fix.