Whois / RDAP / DNS

How WHOIS/RDAP works, DNS basics, reverse lookups

• How WHOIS, RDAP and DNS Work (and How They Differ) WHOIS looks up who registered a domain or IP; RDAP is its structured JSON successor and now the official gTLD source; DNS resolves names to addresses. When to use each.
• What Is Reverse DNS (PTR Records)? Reverse DNS resolves an IP back to a host name using PTR records and in-addr.arpa. Why it matters for mail servers and log analysis.
• DNS Record Types Explained (A, AAAA, CNAME, MX, TXT, NS) What each DNS record type does — A and AAAA for IP addresses, CNAME aliases, MX for mail, NS for delegation, TXT for SPF/DKIM, and PTR for reverse lookups.
• DNSSEC Explained: Signing the DNS How DNSSEC builds a chain of trust with DNSKEY, DS and RRSIG records so resolvers can detect forged DNS answers.
• SPF, DKIM and DMARC Explained The three DNS records that stop others from spoofing your email — how they work together and how to deploy them safely.
• CAA Records: Controlling Who Can Issue Your Certificates A CAA DNS record tells CAs which of them may issue certificates for your domain — a simple guard against mis-issuance.
• DNS TTL Explained: Caching and Propagation What the TTL on a DNS record controls, how it affects "propagation", and how to plan TTLs around a migration.
• What Is an ASN (Autonomous System Number)? An ASN identifies a network with its own routing policy on the Internet. Learn what AS numbers are, how they are assigned and how to look one up.
• BGP Routing Basics How the Border Gateway Protocol stitches thousands of networks into one Internet, what a prefix announcement is, and why route hijacks happen.
• RPKI and ROA Explained How Resource Public Key Infrastructure and Route Origin Authorizations let networks reject BGP route hijacks.