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DNS 101

  • a discover service
  • finds the IP address for a given domain name
  • huge and distributed
  • DNS Root Servers ran by 12 large organizations
  • DNS Root Zone managed by IANA

  • a registry is an organization to maintains the zones for top level domains

  • DNS Client : software on device being used

  • Resolver : software on device or server that queries DNS on your behalf
  • Zone : a part of the DNS database
  • Zonefile : physical database for a zone
  • Nameserver : where zonefiles are hosted

Getting the IP:

  sequenceDiagram
    Client ->> DNS Root Servers: amazon.com
    DNS Root Servers ->> Client : Go to top-level-domain server (.com) server
    Client ->> top-level-domain server (.com) server: amazon.com
    .com server ->> Client : go to nameserver
    Client -->> name server: amazon.com
    name server -->> Client : Here is the IP address

DNS Record Types

Nameserver (NS)

  • enable delegation end to end

root zone --> TLD zone --> domain zone

A and AAAA Records

  • map host names to IP
  • A maps to IPv4
  • AAAA maps to IPv6

Canonical Name (CNAME) Records

When a specific server performs multiple services: - create multiple names and point them to the same A server record - so they point the same IP - can't point to IP address only to names

MX Records

  • used to find mail servers for a specific domain

TXT Records

  • used to prove domain ownership
  • and detecting spam

Time To Live TTL

  • how long a result is cached at a resolver server (probably ISP)
  • used for quicker access