1: Domain Name Service (DNS)

The DNS servers on the Internet play an important part in holding the Internet together. They store the information for all servers, domains and mail sites. They contain routing information for packets received from the international domain name registration servers and databases. Most DNS servers will cache (mirror) the data from the other servers to speed up search times.

2: Brief Terminology

Primary Name Server: ns1.domain.net
Secondary Name Server: ns2.domain.net

Mail Server Primary: mail.domain.net
Mail Server Backup: relay.domain.net

PTR (Pointer Record): Reverse IP with. IN-ADDR.ARPA at its end.
NS (Name Server): Primary and/or Secondary DNS Server.
MX (Mail Exchange): Relays mail to other servers when post server is down.
A (Address Record): Assigns a site domain name to a server IP address.
CNAME (Canonical): Assigns a site domain name to a server domain name.
TTL: (Time to Live): Time in seconds before a cached record is purged.

3: Examples and additional info

Name Field: Contains the domain address for the account (domain.co.uk)
TTL Field: None
Type Field: Contains the type of record transaction. (MX, A, NS)
Data Field: Contains the destination address as follows:

A: Field will contain a server IP address.
MX: Contains an exchange server address and sequence number.
NS: 2 entries will contain the primary and secondary server addresses.
CNAME: Field will contain a server domain name.

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