dns.org

DNS

Table of Contents

• Outline
• Records
  • SOA
  • A and AAAA
  • CNAME
  • ALIAS
  • MX
  • NS
  • PTR
• References

Outline

Records

SOA

domain.com.  IN SOA ns1.domain.com. admin.domain.com. (
                                            12083   ; serial number
                                            3h      ; refresh interval
                                            30m     ; retry interval
                                            3w      ; expiry period
                                            1h      ; negative TTL
)

• SOA stands for Start of Authority
• Name servers can either be master or slaves
• admin.domain.com is an email address. The “@” is replaced with a dot in the email address
• Other settings for managing master and slaves

A and AAAA

ns1                 IN  A       111.222.111.222
ns1.domain.com.     IN  A       111.222.111.222  ;  They are equivalent

@       IN  A       222.222.222.222  ; To refer to the base domain
*       IN  A       222.222.222.222  ; To refer to anything not defined

• AAAA records for IPv6

CNAME

www         IN  CNAME   server1

• Should only be used when there are no other records on that name.
• Comes with some performance losses because they require an additional query to the server
• Recommended to provide an alias for a resource outside of the current zone.

ALIAS

• Some DNS providers like AWS Route 53 provides customized ALIAS records
• With ALIAS records the additional step for looking up the name is done by the server
• Can coexist with other records on that name

MX

        IN  MX  10  mail1.domain.com.
        IN  MX  50  mail2.domain.com.
mail1   IN  A       111.111.111.111
mail2   IN  A       222.222.222.222

• Used to define the mail exchanges that are used for the domain

NS

        IN  NS     ns1.domain.com.
        IN  NS     ns2.domain.com.
ns1     IN  A      111.222.111.111
ns2     IN  A      123.211.111.233

• This record type defines the name servers that are used for this zone

PTR

444.333.222.111.in-addr.arpa.   33692   IN  PTR host.example.com.

• Pointer to a canonical name
• Used define a name associated with an IP address

References

• http://www.learndns.com/pdf/dns101.pdf
• https://www.digitalocean.com/community/tutorials/an-introduction-to-dns-terminology-components-and-concepts
• http://docs.aws.amazon.com/Route53/latest/DeveloperGuide/resource-record-sets-choosing-alias-non-alias.html
• https://serverfault.com/questions/419402/similarities-and-differences-between-cname-record-and-route-53-alias-record