Glossary

Short, plain-English definitions of the networking terms you'll run into.

A

  • A record — A DNS record that maps a hostname to an IPv4 address.
  • AAAA record — A DNS record that maps a hostname to an IPv6 address.
  • AEO — Answer Engine Optimization — making content easy for LLMs to cite.
  • AI bot opt-out — Robots.txt directive blocking AI training crawlers.
  • ALPN — Application-Layer Protocol Negotiation — TLS extension that picks HTTP/1 vs 2 vs 3.
  • Anycast — IP routing trick where the same IP exists at many physical locations.
  • ASN — Autonomous System Number — identifies the network operator that owns an IP range.
  • Autonomous System — An independent network with a unique ASN.

B

  • BGP — Border Gateway Protocol — the routing protocol between Autonomous Systems.

C

  • CAA record — Tells CAs which authorities are allowed to issue certs for this domain.
  • Certificate Transparency — Public append-only log of every TLS cert issued by a participating CA.
  • CGNAT — Carrier-Grade NAT — ISPs share one public IP across many subscribers.
  • CIDR — Classless Inter-Domain Routing — IP ranges as prefix-length notation.
  • CNAME — A DNS record that aliases one hostname to another.
  • CNAME flattening — A nameserver feature that returns A records at the root despite CNAME being configured.
  • CORS — Cross-Origin Resource Sharing — browser policy that gates cross-domain fetches.
  • CRL — Certificate Revocation List — public list of revoked certs from a CA.
  • CSP — Content-Security-Policy — HTTP header that restricts which scripts/styles a page can load.
  • CT log — Certificate Transparency log — public append-only record of every TLS cert issued.

D

  • DKIM — DomainKeys Identified Mail — cryptographic signature proving the message wasn't tampered with.
  • DMARC — Policy record that tells receivers what to do when SPF or DKIM fails.
  • DNS Propagation — The time for DNS changes to expire from caches worldwide.

F

  • FCrDNS — Forward-Confirmed reverse DNS — the IP→hostname→IP round-trip must match.

H

  • HSTS — Strict-Transport-Security — tells browsers to only ever talk to this host over HTTPS.
  • HTTP/2 — Binary, multiplexed evolution of HTTP/1.1 — required for modern web performance.
  • HTTP/3 — HTTP over QUIC — TCP-less transport with built-in TLS and 0-RTT.

J

  • JSON-LD — JSON for Linked Data — the modern way to embed Schema.org in HTML.

L

  • llms-full.txt — Full-content variant of llms.txt — every page's content concatenated for LLM ingestion.
  • llms.txt — Proposed standard listing the AI-readable resources on a site.

M

  • MIME type — Content-type identifier (e.g. text/html) sent in an HTTP response.
  • MX record — A DNS record that tells the world where to deliver email for a domain.

N

  • NS record — Names the authoritative nameservers for a domain.

O

  • OCSP stapling — TLS handshake optimization where the server attaches a fresh revocation proof.

P

  • PTR record — Reverse-DNS record mapping an IP back to a hostname.

Q

  • QUIC — Google-originated UDP-based transport protocol; HTTP/3's carrier.

R

  • RBL — Realtime Blackhole List — a DNS-based list of IPs known for spam/abuse.
  • Registrar — A company accredited to sell domain registrations.

S

  • Schema.org — Structured-data vocabulary embedded in HTML so machines can parse pages.
  • SNI — Server Name Indication — TLS extension that tells the server which hostname is requested.
  • SOA record — Start-Of-Authority — primary nameserver + admin email + zone timers.
  • SPF — Sender Policy Framework — lists which mail servers are allowed to send for a domain.
  • SRV record — Service-location record naming a hostname + port for a specific service.
  • Subdomain — A DNS name that's a child of another domain.

T

  • TLS — Transport Layer Security — encrypts traffic between client and server.
  • TLS 1.3 — The current TLS version — faster handshake, dropped weak ciphers.
  • TTL — Time-to-Live — how long a DNS record stays cached.
  • TXT record — A DNS record that carries arbitrary text — used for SPF, DMARC, and domain verification.

W

  • Webhook — An HTTP POST sent automatically when an event happens.
  • WHOIS — Public registry data for a domain — registrar, creation date, expiry, name servers.
  • WHOIS server — The TLD-specific server that returns registration data for a domain.

X

  • X-Frame-Options — HTTP header that controls whether a page can be loaded in an iframe.