What is the TTL (Time-To-Live) in a DNS record?
The Time To Live (TTL) record defines how long a DNS record should be considered valid before it has to be requested again.
Time To Live examples
A TTL value can be as low as 1 second or as long as 10 years, or anything in between.
These values are all valid.
An example of 1hr time to live value:
ohdear.app. 3600 IN A 217.19.225.103
Or 1 second:
ohdear.app. 1 IN A 217.19.225.103
Or 5 years:
ohdear.app. 157680000 IN A 217.19.225.103
As long as it's a positive natural number - not a decimal/float - it's a valid TTL.
What are TTLs used for?
The Time To Live record defines how long a client - your computer, your webbrowser or your mailserver - can go without having to refresh the DNS record.
If your browser requested the IP address behind ohdear.app
and it found a TTL of 3600, it doesn't have to request a new value for the next 1hr. In other words, it's cached on the client for the next 1hr.
The TTL is used as a means of speeding up DNS requests (by requiring fewer requests) and offloading nameservers, by making sure the client keeps a local copy of the DNS record for a predefined amount of time.
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