DNS (Domain Name System) and DNS records
An SOA(Start of Authority) Record is the most essential part of a Zone file. The SOA record is a way for the Domain Administrator to give out simple information about the domain like, how often it is updated, when it was last updated, when to check back for more info, what is the admins email address and so on. A Zone file can contain only one SOA Record.
A properly optimized and updated SOA record can reduce bandwidth between nameservers, increase the speed of website access and ensure the site is alive even when the primary DNS server is down.
When domain names are registered with a domain name registrar, their installation at the domain registry of a top level domain requires the assignment of aprimary name server and at least one secondary name server. The requirement of multiple name servers aims to make the domain still functional even if one name server becomes inaccessible or inoperable.[11] The designation of a primary name server is solely determined by the priority given to the domain name registrar. For this purpose, generally only the fully qualified domain name of the name server is required, unless the servers are contained in the registered domain, in which case the corresponding IP address is needed as well.
A Domain Name System (DNS) zone file is a text file that describes a DNS zone. A DNS zone is a subset, often a single domain, of the hierarchical domain name structure of the DNS. The zone file contains mappings between domain names and IP addressesand other resources, organized in the form of text representations of resource records (RR). A zone file may be either a DNS master file, authoritatively describing a zone, or it may be used to list the contents of a DNS cache.