DNS 101 (54)

  Amazon Web Services (AWS), Route53

https://www.udemy.com/aws-certified-solutions-architect-associate/learn/v4/t/lecture/2050692?start=0

IPv4=32 bits (4,294,967,296 addresses)

IPv6=128 bits (340,282,366,920,938,463,463,374,607,431,768,211,456 (340 undecillion addresses)

Top Level Domains

  • .com
  • .edu
  • .org

Second Level Domain (Optional)

  • .co.uk
  • .gov.uk
  • .com.au

Top level domain names are controlled by Internet Assigned Numbers Authority (IANA) in a root zone database which is a database of all available top level domains.  You can view this database by visiting: http://www.iana.org/domains/root/db

A Registrar is an authority that can assign domain names directly under one or more top-level domains.  These domains are registered with InterNIC, a service of ICANN, which enforces uniqueness of doamind names across the Internet.  Each domain name becomes registered in a central database known as the WhoIS database

Popular Registrars

  • Godaddy.com
  • 123-reg.co.uk

SOA=Start Of Authority

  • Name of server that supplied the data for the zone
  • Administrator (email address?)
  • Current version of the data file
  • # of seconds a secondary Name Server should wait before checking for updates
  • # of seconds a secondary Name Server should wait before retrying a failed zone transfer
  • Maximum # of seconds that a secondary Name Server can use data before it must either be refreshed or expire.
  • Default # of seconds for the TTL file on resource records

NS=Name Server

  • Name Server records are used by Top Level Domain servers to direct traffic to the Content DNS server which contains the authoritative DNS records.

A=Address

  • Directs a domain name to an IP Address
  • example.com IN A 123.45.67.89

TTL= Time To Live

  • The length of time (in seconds) a DNS record may be cached on either the Resolving Server or the User’s own local PC.  The lower the TTL, the faster changes to records can propagate throughout the Internet.

CNAME=Canonical Name

  • Used to resolve one domain name to another.
  • www.example.com IN CNAME example.com.

Alias

  • Work like CNAME records assigning domain names to the IP of another domain.
  • Difference: CNAME cannot be used with a root domain (zone apex record)
    • You cannot set: example.com IN CNAME elb1234.elb.amazonaws.com.
    • example.com must have either an A record or an Alias record.
  • Proprietary to Route 53
    • Route 53 automatically recognizes changes to Amazon resources (such as an Elastic Load Balancer’s Public IP and automatically reflects those changes in DNS answers for the domain with any additional changes to the hosted zone that contains the Alias record.

Exam Tips

  • ELBs do not have pre-defined IPv4 addresses.  You must resolve to them using a DNS name.
  • Understand the differences between an Alias Record and CNAME
    • Given the choice, always choose an Alias Record over a CNAME

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