We help IT Professionals succeed at work.

DNS TTL value question

mokkan
mokkan asked
on
Hello,

We had  CNAME it was pointing to Porduction and changed the DNS to DR and worked fine.  We have nameserver( resolver in both sides)
Once we changed the DNS back to  Production,  DR resolver was still pointed to DR site, but PROD resolver was pointing to PROD as we exptected.

our TTL value was set to solve to 24 hours.  After 24 hours it worked, but my question is that how come it worked right a way when changed from PROD to DR ?
Comment
Watch Question

Commented:
Where did you make the change, and where did you check it from?

If the check was done from a DNS server with no recent query, it would have picked up the DR response.  It would then cache it for 24 hours which is why it would not revert back as quickly.

For something like that, I would lower your TTL to 15 minutes or something more reasonable for a DR failover.
Distinguished Expert 2017
Commented:
To Matt V's point
The TTLs are enforced by the caching servers.
The authoritative server/s should start responding with the new information as soon as they are made (or within the time for the notify event to reach it and the refresh to be processed.)

Depending on your response to Matt's question on where you saw it.

As to your question, the max delay is 24 hours for users who accessed your site just before you made the change they will experience the longest dealt before failing over.

Usually, your TTL duration iis an inverse proportion to the number if requests seen.
24 hour will have a single request in a day
1 sevond Ttl will mean you will have 86400 requests in a 24 hour period from a single source.

You have to decide the length of time you can tolerate for some users not being able to access your site during the transition.
Top Expert 2015
Commented:
How your DNS is synchronized?

Author

Commented:
Thank  you found the solution