DNS Propagation

Factual Questions
1

I’m switching hosts for my websites; I’ve signed up with the new host and am waiting for the DNS changes to propagate, I guess is the term. I’ll know they’ve propagated (for me) when I go to my URL and see a blank page or 404, because I haven’t uploaded my site to the new host yet.

I don’t really understand what DNS propagation is (in case you couldn’t tell). I want to cancel my hosting services with my old host but not until I’m sure I won’t miss any emails, etc., which means that everyone is seeing the site as hosted on my new host.

My question is this:

When I go to my URL and see a blank page or 404, is that the case for everyone? Or is it possible that I can see one thing and someone else in the US (or the world) can see something else for a period of time, until the DNS changes are “fully” propagated?

2

It can be different for different people. To be simple about it, a user will send a query to whatever DNS server their computer is set to use (usually an ISP server or Google’s). That DNS server will then query whichever DNS server “owns” the domain to get the IP address translation. Along with that they will get a timer stating the maximum amount of time the ISP server can cache that data.

So at that point the ISP DNS server has the information cached, and the next person who queries will get the cached data, the ISP server will not query again until it expires.

So if, say, Comcast’s servers got information right before the DNS change was made, they’d have the old information until the cache expired–but maybe Verizon’s servers hadn’t asked in a long time and someone from there asking right after the change would get the new one.

3

Thanks for the clear explanation! Much appreciated.

4

If you want to check the propagation state:

https://geopeeker.com/ will let you see what it looks like from 6 countries.

Monitor Website Uptime and Availability Worldwide: Site24x7 Tools will show you numbers (load time, file size, etc.) for like 40+ locations.

Or just wait 2-3 days and most of the civilized world should get it…

5

Your DNS should include an option for Time-To-Live (TTL) with drop-down options or a field for minutes. If you know you’re moving a domain, I recommend lowering that value a day or so ahead of time, so propagation happens as quickly as possible.

There’s a lot of info in your DNS records though, and you’re asking about email, which isn’t the A/C records that your web browser uses. You want the MX (or Mail eXchange) record to be updated. (Which still works the way dzeiger says, just more difficult to determine yourself).

There’s still going to be a TTL value for them too, so provided everyone’s actually using it properly, whatever it’s set to is pretty much how long you need to wait. Maybe use https://mxtoolbox.com/ if you want more info

6

Another point is that if you are trying to see the result of DNS change right away - probably not. Your own PC also caches DNS results. Obviously, you don’t do a fresh lookup of the site name every time you click on a link.

Open a command prompt (DOS box) and type
IPCONFIG /DISPLAYDNS
this shows detail about your local DNS cache.
(I do this and my DNS shows typically TTL of 18)

To clear the cache, type
IPCONFIG /FLUSHDNS
Now, the next time you try to access a website by name, your PC will go and do a fresh lookup of the name to IP conversion. If the DNS server you’ve defined for your PC has timed out and/or updated, you will get the new value.

The general warning is it can take an hour or up to 24 hours to propagate to the whole world, but generally I find 5 to 10 minutes is plenty for a change to take effect for the people who need it.