Question : How ttl helped to propagate dns record

Hi

As far I know, if you set a short ttl , it will help to propagate dns record worldwide quickly and will be helpful for service like failover..


so, in my zone record, i have set  $TTL 1m

so i am guessing 1m = 60 seconds and the new changes should propagate after 1 minutes.

then when i ping example, www.intranet.mydomain.com  

Some Isp showing accurate result mail.mydomain.com but some isp showing Old result which is ns1.mydomain.com

omm I am guessing , its because of something Dns propagation delay from those ISP

so if thats the case then whats the point of ttl, i thought ttl will force dns record to update after 1 minutes(as you set on zone record)

suppose if i have a failover service, those Isp where dns records is not updated , any clients from those isp would not be able to take advantage of my failover service

Am i thinking right or am i missing something Or there is something else i need to change ??

Answer : How ttl helped to propagate dns record

>  i thought ttl will force dns record to update after 1 minutes(as you set on zone record)

It does, but it does not apply retroactively.

That means if your TTL was 2 days any server that had queried that record would still remember it for 2 days. They would only receive the updated TTL next time it had to ask your server (when the cached version expired).

Chris