SOA Records Explained Simply

What is an SOA Record?

An SOA (Start of Authority) record is like the birth certificate of your domain. It contains essential information about your domain's administration, including who's responsible for it and how often it gets updated.

Format:

@ IN SOA primary-ns admin-email (
    serial      ; Serial Number
    refresh     ; Refresh interval
    retry       ; Retry interval
    expire      ; Expiration time
    minimum-ttl ; Minimum TTL
)

Real-world example:

example.com. IN SOA ns1.example.com. admin.example.com. (
    2024030501 ; Serial: YYYYMMDDNN
    3600       ; Refresh: 1 hour
    1800       ; Retry: 30 minutes
    604800     ; Expire: 1 week
    86400      ; Minimum TTL: 24 hours
)

Simple Explanation

Think of an SOA record like a book's publishing information page:

The publisher (primary nameserver) who's responsible for the book
The editor's contact (admin email) for questions or issues
The edition number (serial) to know if you have the latest version
Publishing schedule (refresh, retry, expire) for updates
Copyright duration (TTL) for how long information can be reused

Just like you need this information to manage a book's publication, DNS systems need SOA records to manage and update domain information properly.

Understanding SOA Fields

✓
Primary NS
The primary nameserver for the domain (e.g., ns1.example.com)
✓
Admin Email
Domain administrator's email (@ replaced with ., e.g., admin.example.com)
✓
Serial Number
Version number, usually in format YYYYMMDDNN
✓
Refresh
How often secondary servers check for updates (e.g., 3600 = 1 hour)
✓
Retry
How long to wait before retrying failed refresh (e.g., 1800 = 30 minutes)
✓
Expire
Maximum time secondary servers should retain data (e.g., 604800 = 1 week)
✓
Minimum TTL
Default TTL for negative responses (e.g., 86400 = 24 hours)

Important Things to Know

•
One SOA Per Zone
Each DNS zone must have exactly one SOA record - no more, no less.
•
Serial Number Updates
Always increment the serial number when making zone changes.

Common Mistakes to Avoid

⚠️
Forgetting Serial Updates
Not incrementing the serial number prevents secondary servers from getting updates.
⚠️
Incorrect Time Values
Setting refresh, retry, or expire times too low can overload your DNS servers.
⚠️
Invalid Email Format
Using @ in the admin email instead of a dot (.) will cause parsing errors.

Quick Tips for Success

✓
Use Standard Time Values
Stick to common refresh (3600), retry (1800), and expire (604800) values unless you have specific needs.
✓
Document Changes
Keep a log of serial number updates and what changes were made.
✓
Regular Verification
Periodically check your SOA record to ensure all values are correct and up to date.

Beep beep... Loading...