DNS propagation is a lazy myth
Someone (probably your ISP or registrar) hosts your DNS for you. Typically they'll have some sort of master server and at least one slave. Updates are made to the master and, within a reasonable timeframe, find their way to the slaves (if you have a reasonable provider, their slaves should update almost instantly).

The rest of the problem is DNS caching - when you query a DNS record, you'll be using a resolver somewhere to do the work of getting the data for you and giving you back the result you want. This cache is generally provided by your ISP, though you can run your own.

In order to cut down on the number of queries resolvers make, they cache a record for a certain amount of time. This time-to-live (TTL) is set by the person who owns the domain, and can be anything from zero seconds (no caching) to days or even weeks.

If you had a long TTL on the old record, and it got cached by someone's ISP's resolver, they'll get the old server's IP address until that record expires. Once the record expires, or if they're using a resolver that hasn't cached the record, they'll get the new one immediately.


To avoid the problem of getting one site or the other, you need to check that changes on the master cause the slaves to update immediately (DNS NOTIFY, or some other mechanism). Then, lower the TTL to a few minutes (or even a few seconds) far enough in advance of the change in server that anything which cached the old TTL will expire (eg, if your old TTL is 12 hours, you need to lower the TTL at least 12 hours in advance). Once that time has passed, change the DNS record. Everyone will be looking at the new site in a matter of minutes (depending on how long your lowered TTL is).

"DNS Propagation" is what people who forgot to do this tell irate customers/managers. It's bullshit.
( le brian, Tue 8 Sep 2009, 13:44, 1 reply, 16 years ago)

Blimey
thats technical stuff for a simple salesman like me! Thanks though - I may well be copying & pasting a lot of your post in to an email to the provider very soon!
( lkjshaglkasjdhglkhjz lkcvl; g;aodh;owih, Tue 8 Sep 2009, 14:11, Reply)