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Definition

The Domain Name System (DNS) is a hierarchical decentralized naming system for computers connected to the Internet 1. It allows to access servers by name instead of an IP address which is hard to remember.

Public DNS

Google DNS: 8.8.8.8 or 2001:4860:4860::8888

Resource Record Format

All RRs have the same top level format shown below:

<NAME> <TTL> <CLASS> <TYPE> <RDLENGTH> <RDATA>

with

Resource Record Types

DNS Type Return Type Application
A IPv4 address map domain to 1 static IP
AAAA IPv6 address map domain to 1 static IP
ALIAS Domain name map domain to domain
CNAME Canonical name map 1 domain to 1 domain
DNAME Delegation name map domain + subdomains to domain
NS Name server delegate to other DNS
SSHFP Public key provide authentication
MX URL Mail exchange server
URL URL redirect (HTTP 301) domain to URL

DNAME

The DNAME record provides redirection for a subtree of the domain name tree in the DNS 2. Note that a DNAME entry that maps mydomain.com to public.com will also map sub.mydomain.com to sub.public.com.

ALIAS

The ALIAS type is not part of the DNS standard and should only be used to map an Apex domain to another domain because CNAME cannot be used for this task.

Rules for setting up a DNS entry

Propagation Time

Changes propagate within the network in about 24 hours. TTL of records: 5 minutes to 24 hours.

DNS Softwre

Linux: dig DOMAIN, host DOMAIN, nslookup DOMAIN

References


  1. RFC 1035, Domain Names - Implementation and Specification , 1987

  2. RFC 6672, DNAME Redirection in the DNS, 2012