What is an SOA record?
The start of authority (SOA) of a domain is a type of domain name system (DNS) record that stores information about that domain in the form of a zone file. A zone file is created when a new domain is registered and the details about that domain are made available. The SOA record holds information about how your zone should propagate in the secondary name servers.
What is a DNS zone?
DNS records help us translate a domain name into its corresponding IP address. The global DNS generally distributes a domain into different zone files, with each zone being handled by a specific organization or an administrator. Handling the DNS namespace as multiple zones helps with getting granular control over its components. Each zone file can contain more than one subdomain, and each server can hold multiple zone files.
How does an SOA record work?
When a client-server requests a specific domain name, the DNS server does a zone check to identify the server that contains its zone file. The server that holds the zone file is also termed the authoritative name server (NS). This NS then resolves the DNS lookup by providing the IP address of the hostname.
The SOA record is usually helpful when a zone transfer happens from the primary server to its corresponding secondary server. The primary server holds all of the details about a particular domain, including the IP address of that domain. The secondary server holds a read-only copy of the primary server. The secondary server periodically requests the latest copy of the domain details from the primary server, during which time a zone transfer happens. At this stage, the SOA record gives an idea about whom to contact (e.g., an administrator), the interval time between each refresh/update request, and other details.
Example of an SOA record
Zoho Toolkit offers a built-in line of DNS record lookups. One can easily find the details of a particular domain with just one click. Enter the domain/ hostname for the SOA record that needs to be looked up. The result would contain the hostname, server name, TTL, serial number, refresh, retry, and expiry rate of that domain.
|Host Name||Server name||TTL||Serial no||Refresh rate||Retry rate||Expiry rate|
|abc.com||ns1.acdns-1.com||1800sec||1||7200sec||900 sec||1009500 sec|
Components of an SOA record
A typical DNS SOA record consists of the hostname, server name, TTL, serial number, refresh, retry, and expiry components.
Serial number: This numerical value gets updated whenever there's a change in the record. Generally, every time a change occurs, the value changes by increments of one, and the value can go up to 2^32.
Refresh rate: This is the amount of time the secondary server waits before requesting the primary server for the updated records, and is calculated in seconds.
Retry rate: This is the amount of time the secondary server takes before retrying a failed request.
Expiry rate: The amount of time until a secondary server considers the SOA record to be authoritative. If no zone transfer happens before the expiry period, the zone file is considered to be too old and wouldn't be used further.
Server name: This is also called the primary server/MNAME. The secondary servers that maintain copies of the records on the primary server receive an update to the zone through the primary server. The records of the primary server stay as a read-only copy on the secondary server.
TTL: Time-to-live tells the server how long the data can be stored in the cache before its next update.
Frequently Asked Questions
Can I edit my SOA record?Yes, the SOA record can be edited, but extreme care should be taken while doing so because it could directly impact the domain's performance. It's recommended to always make a backup before making any changes to this file.
What's the difference between an SOA and an NS record?An SOA record contains useful information about a DNS zone, such as the administrator, refresh, retry, and expiry rate, whereas an NS record helps to identify the server on which the DNS records exist.