DNS changes -- how long does it REALLY take them to propagate?

It can take that long but I usually find it is updated in 2 - 4 hours or so, they just cover themselves I guess.

Agreed. They usually say 24-48 hours, but as per barney_parker and MojoTech, the time increases the further you go round the world.

If I make DNS changes here in the UK, most UK ISP's are updated pretty quickly, some < 15 minutes. Generally though, I find most around the world are done within 24 hours.

Lee

1-2 hours for national
2-3 hours for continent
up to 48 for the world !!

chernavsky, the DNS propogation depends on the TTL = Time to live for your DNS records. Typically new domain names take about 24 hours to propogate throughout the www but this also depends on your DNS hosts servers and network. If you've configured your client or adsl connection to use the same nameservers as your domain host then you should see the records and updates as soon as they are done, but the rest of the www will take take to update.

Personally, i think the whole 48 hours hting is a bit of back covering!

I've made DNS changes and seen them available in other continents within a few hours.  maybe i've been luck with timing or something.

To be hoest though, unless you're dealing with sites that are pretty large and international, it shouldn't be an issue.  If you are dealing with something that large, then make sure you issue users a warning that this maintenance is taking place....

It all depends on how often the DNS server hosting your domain is configured to "sync" with the root servers. Once the synchronization to the root servers takes place, other servers need to "sync" with the root servers in order to obtain your new DNS information.

The reason they say it can take up to 48 hours is because some servers are intentionally configured to "sync" at longer intervals. This means that while you might be able to resolve the address, other people will not be able to until the process is complete.

Here's a little more info:
http://webhosting.devshed.com/c/a/Web-Hosting-Articles/What-is-DNS-propagation-and-why-does-it-take-so-long/

This is the correct answer (posted by beatleuk):

> the DNS propogation depends on the TTL = Time to live for your DNS records.

There are a few exceptions to that because not all systems obey TTLs set on records. AOL and a few other other large mail services are prime examples of that, in those cases you can expect a change to take anything up to a week.

However, propagation in all other cases is dependent on the TTL set on the record(s). In the case of brand new domains there is no existing TTL, and therefore no wait time because everyone who needs the name must check in with the authoritative servers (directly or indirectly).

Chris

> The reason they say it can take up to 48 hours

I've long held the belief that they say 48 hours because either:

They don't understand why it might not be

Or

They don't want to explain what it might be

You can put that down to being lazy, or you can call it a safety value, if it's not working after 48 hours then something is quite wrong.

Chris

You are referring to a *new* domain.  It should not take 48 hours for the root zones to get the update.

Amendment:  unless of course there is the administrative overhead of the registrar you are using to complete the registration.

TTL at this point has nothing to do with the issue.

Local DNS servers don't "sync" to the root servers.  That's not how DNS works.

There is one more possibility for the "48 hours" thing.

Some companies may be a bit slow to make the change in the first place, so the 48 hours is occasionally nothing to do with DNS propagation and everything to do with internal process. That never stops "DNS propagation, 48 hours, kthxby" being quoted as the reason however inaccurate.

Chris

Oh nevermind, that's what Jesper said, I need a bigger refresh button :)

Chris

Thanks to everyone for the useful comments.