DNS question

[TechMan]

Hi,

I have the following experience so far regarding DNS update.

1. When I change DNS of a domain for the time being it continues to point to existing site
2. After some time, website stops showing i.e. downtime. It neither shows old nor new site.
3. Then after around 24 hours (after DNS propagation) new site starts to show up.

But a person told me just now that when you update DNS then no downtime occurs at all. That is step 2 I described above doesn't happen. When you update DNS, old website continue to show up and as soon as DNS propagation is complete then new site shows up, without any downtime. Is this true?

Thanks

 

[Poohnix]

Yes.

There is no downtime.
The old web site is shown as long as the DNS server used by the person visiting has the old record.
As soon as it fetches the new record, the new web site is shown.

How long it takes before a caching dns server fetches the new record, depends on the DNS record TTL (Time-To-Live) BEFORE the DNS update. (And of course weather that DNS server at all had a cached record or not - otherwise it's fetched as soon as the user tries to visit the web site, and then he of course ends up on the new site, since his DNS server had no record of the old.)

 

[TechMan]

Yes.

There is no downtime.
The old web site is shown as long as the DNS server used by the person visiting has the old record.
As soon as it fetches the new record, the new web site is shown.

How long it takes before a caching dns server fetches the new record, depends on the DNS record TTL (Time-To-Live) BEFORE the DNS update. (And of course weather that DNS server at all had a cached record or not - otherwise it's fetched as soon as the user tries to visit the web site, and then he of course ends up on the new site, since his DNS server had no record of the old.)

Ok then may be I am confusing downtime with something else because I have also asked other people and no downtime happens.

 

[Poohnix]

Well, the only reason you would see any down time, is if you take down the old web site at the same time you change DNS.

 

[Profithost]

You only see the old location because your provider needs to update. In the end there is no global downtime. New visitors will see the new location immediately. Its called DNS population.