DNS take important part in internet world as resolver for domain. The problem came when we think something wrong with it. Need to examine which server is in trouble.
From this picture :

There is two dns servers :

202.146.178.4
208.67.222.222

In windows we can check which dns server that work well using nslookup.
Steps :
1. Click start -> run
type  cmd [...]

Click here to read more from dns server