TTL is Time-To-Live, a measure in seconds of how long a DNS record (such as a name-to-address mapping) is valid.
How to configure
E.g. on Directnic.com,
- Find your domain ("My Services" menu, "Domains" item, search for your domain by name, click on it)
- Select the DNS: Manage button
- Scroll to the bottom to DNS Time To Live Value
- Set the number to as low as you can (600 was the minimum as of 2019-02-24)
- Google's public DNS at 22.214.171.124/126.96.36.199 respects TTL settings as low as 0, effectively supporting a setting for 'do-not-cache'.
- OpenDNS's public DNS at 188.8.131.52/184.108.40.206 has a minimum TTL setting of about 10 seconds.
Observing the Effect of DNS TTL
On a terminal with the dig and watch programs, run a per-second lookup of the domain under test:
watch -n 1 "dig +short test1.indieweb.org @220.127.116.11"
As you then update DNS IP settings, the results displayed should change to the new IP setting within the seconds specified in the TTL.