Networking / Beginners

Resource Records (RR)

A DNS resource record (RR) contains all the information about a domain name system. It defines all the attributes for a domain name such as an IP address or a mail route.

A DNS RR has six fields:

<NAME>, <TYPE>, <CLASS>, <TTL>, <RD Length>, and <RDATA>

These fields are explained in the following list:

  • Name. This field specifies the DNS name, also known as the owner name, to which the RR belongs.
  • Type. This field is a 2-byte value that specifies the type of the resource that is defined in the resource record. This field is necessary because a DNS name can have more than one type of RR.
  • Class. This defines the protocol family for the RR record. For example, IN, which stands for Internet.
  • Time To Live (TTL). This field is the time, in seconds, for which a name server can cache an RR. A zero TTL implies that a server should not cache the RR.
  • RD Length. This field is the RDATA field's length in octets.
  • RDATA. This field is a resource data field and is the value to which the entity specified in the NAME field maps. It is unique for each type of RR.

Common DNS Resource Records

Record TypeDescriptionUsage
AAn address recordMaps FQDN into an IP address. For example,
Mail IN A 172.100.100.1
Login IN A 172.100.100.2
PTRA pointer recordMaps an IP address into FQDN. For example,
1.100 IN PTR mail.example.com.
NSA name server recordDenotes a name server for a zone. For example,
IN NS ns1.abc.com.
IN NS ns2.abc.com.
SOAA Start of Authority recordSpecifies many attributes concerning the zone, such as the name of the domain (forward or inverse), administrative contact, the serial number of the zone, refresh interval, retry interval, and so on.
CNAMEA canonical name recordDefines an alias name and maps it to the absolute (canonical) name. For example,
POP IN CNAME mail
MXA mail exchange recordUsed to redirect e-mail for a given domain or host to another host. For example,
xyz.com IN MX 0
mail.abc.com
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In this tutorial:

  1. Linux Other Network Servers
  2. Setting the FTP User Account
  3. Configurations File for FTP Server
  4. ftpusers
  5. Anonymous FTP
  6. Using Proper Password and Group Files
  7. Anonymous FTP Warnings
  8. Sendmail
  9. Sendmail Security
  10. Domain Name Service
  11. Domain Name Space
  12. Services Offered By a DNS Server
  13. DNS Transactions
  14. BIND
  15. BIND Configuration
  16. Resource Records (RR)
  17. Start of Authority (SOA)
  18. nslookup
  19. BIND Security
  20. Host Name Spoofing
  21. Running BIND with Least Privileges
  22. DNS Security Extensions (DNSEC)
  23. SAMBA
  24. SMB Protocol
  25. Mounting the SMB File System
  26. SAMBA Security
  27. Server-Level Security