Internet Tools

BGP is the protocol that routes traffic across the internet's 80,000 autonomous systems — and its trust model is why a misconfiguration at a small ISP took down Cloudflare, Amazon, and Facebook for two hours. Here's how BGP works, how anycast CDNs use it, and why RPKI is the partial fix.

Every publicly-trusted SSL certificate issued since 2018 is recorded in public, cryptographically verifiable logs — and browsers won't trust a certificate without proof of logging. Here's why Certificate Transparency exists, how CT logs let you discover every certificate ever issued for your domain (including ones you didn't request), and how CAA records complement CT for security monitoring.

Most DMARC records are at p=none — monitoring mode with no actual protection. Here's the safe four-phase path from p=none to p=reject, how to read aggregate reports, the February 2024 Google/Yahoo requirements, and common mistakes.

A single high-latency traceroute hop usually isn't a problem. Asterisks don't mean the hop is down. Here's how to read traceroute output, identify where latency is actually introduced, and distinguish ICMP rate limiting from real network issues.

A DNS query might return an answer cached by your browser, your OS, your ISP's resolver, or a CDN's resolver — and each cache has a different expiry time. Here's the four-layer DNS caching chain, why the TTL on your old record controls propagation speed (not the TTL on the new one), how to read the remaining cache TTL from dig output, negative caching (why "doesn't exist" responses are also cached), and why Anycast DNS means propagation isn't geographically simultaneous.

A PTR record can say anything — anyone who controls a server can configure their reverse DNS to claim any hostname. FCrDNS (Forward-Confirmed Reverse DNS) verifies authenticity by checking that the PTR hostname resolves back to the original IP. Here's how to read ISP and datacenter naming conventions in PTR records, how reverse DNS reveals email header forgery, and why PTR record changes can indicate BGP hijacking.

A WHOIS lookup that once showed a domain owner's name, address, and phone number now typically returns "REDACTED FOR PRIVACY" — the result of GDPR-driven policy changes that affected WHOIS globally, not just for EU registrants. Here's why this happened, what information remains visible after redaction, how RDAP is replacing the decades-old WHOIS protocol with structured JSON output, and whether paid "WHOIS privacy" services still add value.

Learn how ping works, how to read RTT and packet loss results, when a ping timeout doesn't mean a server is down, and how to use a free online ping tool for network diagnostics.

A domain that never sends email is, paradoxically, an easy spoofing target — recipients have no way to know "this domain never sends mail" without DMARC explicitly saying so. Here's why p=reject can be applied immediately (with zero risk) to parked/non-sending domains and subdomains, how sp= protects subdomains separately from the primary domain's policy, and why BIMI specifically requires p=quarantine or p=reject, not p=none.

Learn how DNS works, what record types mean (A, MX, TXT, CNAME, NS), how to diagnose common DNS problems, and how to use a free DNS lookup tool to check any domain's records.