[Techtalk] Stupid DNS questions

[Mary]

On Mon, Mar 08, 2004, Kai MacTane wrote:
> I must confess, I don't quite get the TTL.

I think that's for caching name servers that aren't authoratative.

So if a user of ns.example.com, which is totally unrelated to
puzzling.org, requests data for puzzling.org (because they're visiting
the web page, say), ns.example.com will cache that data for the length
of the time to live (24 hours in the case of puzzling.org). If another
user requests the puzzling.org data from ns.example.com within 24 hours,
then ns.example.com will not return to the authoratative puzzling.org
nameservers for that data.

This is why people are concerned about ttl when their site is moving
IPs: regular users will not see the new IP until the time to live is up,
if they did a request just before the change. In this case, people
normally drop the time to live to something really short a few days
before a move.

-Mary