After any change to Nameserver or DNS zone settings, it may usefull made a check, there are online several tool, here it is some:
DNS Health by Pingdom
A comprehensive test for global DNS configuration. Can be used for undelegated DNS servers
Zonemaster
Another comprehensive test, complete and fully configurable.
Into DNS
Very easy for a quick check.
DNS Propagation
An inutitive webtool for check DNS and IP propagation.
What's my DNS
Another easy global DNS propagation checker.
Dig Web Interface
Extensive and very professional web interface to dig for doing online dns / nameserver query.
Remember, every single time you make a change to the DNS servers of your domain, or you modify any DNS record, you have to wait for the propagation of this data to be effective.
Propagation is the time it takes for each of the internet backbones to be updated with your new DNS information.
It's not linear: these data travel from one DNS server to another, and is influenced by the policy of every single server. So it may happen that a user see new DNS data in few minutes, while another user (with different connectivity and DNS server) take many hours or up to 5 days.
