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Definition
DNS TTL, or Time To Live, is the amount of time a DNS resolver is allowed to cache a DNS record before it checks for a fresh answer from the authoritative DNS server.
TTL affects how quickly changes to DNS records may be noticed across the internet. A shorter TTL can help changes take effect sooner, while a longer TTL can reduce repeat DNS lookups but may delay record updates.
Key Takeaways
- DNS TTL controls how long other networks may keep a cached copy of a DNS record before checking for an updated version.
- Lowering TTL before a planned DNS change can reduce the time some visitors or mail servers keep using old records, but it does not remove all propagation delay.
- TTL settings matter most during website launches, hosting migrations, email platform changes, SSL updates and domain or DNS troubleshooting.
Quick explanation
What DNS TTL Means in Plain English
Key DNS Terms Used in This Guide
TTL is easier to understand when you know the other parts involved in a DNS lookup. These are the main terms that appear when discussing DNS record changes.
- Authoritative DNS server
- The DNS server that holds the official DNS records for a domain. When cached answers expire, resolvers check back with this source.
- DNS resolver
- A system, often operated by an internet provider, network or public DNS service, that looks up DNS records for users and may cache the result.
- DNS propagation
- The period during which DNS changes are gradually noticed by resolvers and networks. TTL is one factor, but provider behaviour and caching also play a role.
How it works
How TTL Affects a DNS Lookup
Process
What Happens When a DNS Record Changes
A DNS record change is not just one action. It moves through several layers of DNS infrastructure before every user sees the same result.
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The record is updated at the DNS provider
A new value is added to the DNS zone, such as a new A record for website hosting or a new MX record for email delivery. The authoritative DNS server now has the new answer.
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Resolvers continue using cached answers where allowed
If a resolver recently looked up the old record, it may keep using that old answer until the previous TTL period ends. Users behind that resolver may still reach the old destination.
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Resolvers request the updated record after cache expiry
Once the TTL expires, the resolver should query the authoritative DNS server again. It then receives the updated record and caches that new value for the next TTL period.
Simple DNS TTL Example
In many DNS zone files and DNS interfaces, TTL is shown in seconds. The examples below show three records with different TTL values.
example.com. 300 IN A 203.0.113.10
www.example.com. 300 IN CNAME example.com.
example.com. 3600 IN MX 10 mail.example.com.A TTL of 300 seconds means five minutes. A TTL of 3600 seconds means one hour.
TTL Does Not Make DNS Changes Instant
Business impact
How TTL Can Affect Websites, Email and SSL
Low TTL vs High TTL
There is no single perfect TTL for every record. The right setting depends on how often a record changes, how critical the service is and whether a migration or launch is coming up.
| Consideration | Lower TTL | Higher TTL |
|---|---|---|
| Change speed | Can help resolvers refresh records sooner after a planned change. | Old cached values may remain in use for longer after a change. |
| DNS query volume | May increase repeated DNS lookups because caches expire sooner. | Can reduce repeated lookups because resolvers keep answers longer. |
| Best suited to | Upcoming migrations, testing windows or records likely to change soon. | Stable records that rarely change and do not need rapid updates. |
Planning
When TTL Should Be Reviewed Before a DNS Change
Common TTL and DNS Record Mistakes
DNS changes can affect several services at once. These mistakes are common when records are edited quickly or without a clear migration plan.
Changing records without checking the existing TTL
Do this instead
Review TTL values before changing DNS. If a critical change is planned, lower the TTL in advance and allow the old cache period to expire first.
Assuming DNS only affects the website
Do this instead
Check the full DNS zone, including MX, SPF, DKIM, DMARC, verification records and service-specific CNAME records before editing anything.
Deleting old records before the new service is tested
Do this instead
Where practical, prepare and test the new environment first. Keep rollback options available until the new website, email or service is confirmed as stable.
DNS TTL Review Checklist
Use this checklist before a planned DNS update, especially when moving a website, changing email platforms or connecting a new service.
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Document current DNS records
Record the existing A, CNAME, MX, TXT and verification records before making changes. This helps with troubleshooting and rollback if needed.
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Review TTL values before the cutover
If a record has a long TTL, reduce it well before the change where appropriate. Give the previous cache period time to expire.
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Test connected services after changes
Check the website, SSL, forms, email sending, email receiving and third-party integrations after the DNS update has been made.
Troubleshooting DNS Record Changes
If a DNS change appears not to be working, the issue may be caching, an incorrect record, the wrong DNS provider or a connected service still using old settings.
Some users see the new website and others see the old one
Likely cause
Different DNS resolvers may have cached the old A record or CNAME for different lengths of time.
Solution
Check the authoritative DNS record, confirm the TTL, test from multiple networks and allow time for caches to refresh. Avoid making repeated changes while propagation is still in progress.
Email stops working after a DNS change
Likely cause
MX records or email authentication records may have been changed, removed or cached incorrectly.
Solution
Review MX, SPF, DKIM and DMARC records. Confirm the email provider's required values and test sending and receiving after changes are applied.
A verification record is not being detected
Likely cause
The TXT or CNAME record may be in the wrong DNS zone, entered incorrectly or still affected by cached data.
Solution
Confirm which nameservers are authoritative, check the exact record name and value, then allow time based on TTL and provider behaviour.
Do it yourself
Can You Change DNS TTL Yourself?
Our approach
How We Approach DNS TTL and Record Changes
DNS TTL FAQs
These short answers cover common questions about TTL, DNS propagation and record changes.
What is a good DNS TTL value?
Does lowering TTL speed up DNS propagation?
Can TTL affect SEO?
Need Help Reviewing DNS Before a Change?
If your website, email or domain is being moved, changed or repaired, we can review your DNS records and help plan the change properly. Start with a conversation so we can understand what is connected and what needs to be protected.