OK ok, I agree its one of the BIGGEST confusions of world!
MOST of web host state that if you have changed your domain’s name server’s to there’s server then also it will take around 24-48 hours for DNS changes to propagate.

WRONG!!!

Correct sentence would be
If you have changed your domain’s name server’s to theirs server then also it might take around 24-48 hours for DNS changes to propagate.
no no…Still that’s just a bit of “truth!”
What I mean to say it’s just creates a wrong image of DNS working in eyes of a newbie. Let me be clear in one thing – There is NO such think like propagation between world dns server…blah..blah blah….that’s just a wrong picture.
Now lets think over it and shoot it!

Question:

What happens when you change name servers of your domain or either change the DNS records like A, MX etc?

Answer:

Case 1 – You changed any DNS Record

You modified a DNS record and hit submit key
Now all these are done on Primary Name server (generally ns1)
as soon as you change, SOA serial number on Primary name server increases its value. Now it’s a simple thing that secondary name servers keep on checking primary name server for SOA serial number up gradation as per “refresh” parameter of SOA.
When as per “refresh” secondary ns will check primary ns and detects SOA serial is increased, it will initialize a XEFR Zone transfer (XEFR – incremental of AXFR) and thus this will transfer the change to secondary name server. And thus ALL servers hosting DNS zone of your domain are updated.
BUT that was strictly behind the scene work, and here forward screen is a bit frustrating!
Lets say if I had a dns record for domain.com pointing to 11.22.33.44 and it had TTL of 3600 (1hr), my friend in same city opens it he gets through the site and finds issue with server, and I just change the hosting to other server by modifying A record to my other server say 44.33.22.11 and then here’s complexity.
I am using 2 name servers and then just say refresh value in my SOA is 300 (5mins)
now just after changing name server’s I ask my friend in other location to check site, here it is possible he sees site up, possible he sees down. As e.g. if at time of opening he hits primary DNS revolver, he will get new server’s ip BUT incase he hits secondary DNS server before 5mins of my updating to primary ns, then he will get to old faulty server and thus site will be down for him.
On other side, site will be down for 1hr for my friend who was in my city (who informed me) because as soon as he opened my site, old site’s record was cached in ISP’s revolver and thus he will keep on getting to old server until record expires as per TTL.
Thus two things effect – TTL & SOA (both, are you sure….no no…read more carefully)
That kind of working is just followed by most of private server cluster’s (common in corporate offices) but these days most of world’s dns host use advanced method and “push up” changes to secondary (slave) name servers as soon as changes are done on primary ns. This means they initialize a XEFR zone transfer without looking at refresh periods

Case 1 – You changed Name Servers of a domain

Now here two factors affect propagation largely old friend TTL & Domain Registrar
TTL affects same as done in last case as dns records get cached on ISP’s end (or any other local revolver) and thus lookup gives old records.
Registrar – yea! our domain registrar. In simple words its quality effects DNS migration! Lol
Ok how? – here it is
There are MANY poor “companies” who call themselves registrar and fool people! We can call them reseller but believe me in domain registration market you will find LOTS of good quality of resellers.
They technically effect situation as poor companies make users to operate on a CMS! Yup
They make user to login at a CMS and give a feel of domain control panel using forms!!!
This means when one changes name servers, the data is recorded BUT not comes in effect because it’s recorded! As soon as you fill up that form, it goes to company Tech. People and they modify name servers BY hands (through original control panel of a good Registrar). This makes an average delay of 5-6 hours in name server updating. Generally small web hosting company use this kind of setup, in which they registrar domain for customers and give customers a feeling that he is managing domain himself.
On other side if you use an Original Domain Registrar or a reseller having proper setup of this stuff, you will see changing name servers will take place in less then 10 seconds!
So this is actually DNS Propagation – propagation of DNS Zone file across DNS servers (hosting that domain….). I am ending up with few FAQ’s regarding the subject. Feel free to as if any confusion is still there.
[faq list DNS Propogation]
[ratings]
NOTE: You can download this post as pdf directly by clicking here