Say I have a DNS entry with a Time to Live set to 1 day or 86400 seconds, and I update it's destination IP, I wonder how long it would take in a worse case scenario for an end user until his he gets the new IP.
My assumption is that it could actually take 72 hours before the end user receives the new IP address. Is this right? Does the caching in multiple nodes allow this to happen?
This is based on the assumption:
- The nameserver updates the entry immediately.
- The ISP, user router and user computer are all caching the DNS entry.
- All the nodes are respecting the set TTL. They look at the TTL as a timeout, not an expiration date.
- At t=0, the nameserver updates the entry.
- At t=23:59hours, the user router asks the ISP for the latest IP.
- At t=24, the ISP gets the new entry.
- At t=47:59hours, the user computer asks the user router for the latest IP.
- At t=48, the user router gets the new entry.
- At t=71:59, the user computer asks the user router again, which is finally up to date.