DNS

when we want lookup something or  enter a web page on computer.first we should input a keyword,it could be a name .for example if you input ‘google’,than you can go to the google webpage. here, ‘google ‘is called domain name. Every domain name have a corresponding IP address. so www.google.com can translate to address 74.125.79.99 .
we also can use IP address to go to a webpage. but domain name is more easy to ramember.This is how domain system is working in our life.
when we input a domain name,the network have a server that can automatically resolve the corresponding domain name IP address , this is the DNS server . but sometime the DNS also has a error. For example ,a domain name resolves to the wrong IP address,or do not know the IP address corresponding to a domain name,we cant access the site throught the  domain name.

Than we can use nslookup to  judge if it is a DNS resolution failure.

The first step: Make sure your system is windows 2000 and windows xp operating system above, and then “Start – “Run -> enter CMD “into the command line after the carriage return.

Step two: Enter the nslookup command, press Enter to enter the DNS resolution query interface

The third step: the command line window will display the current system used by the DNS server addresses, such as the author of the DNS server IP is 202.106.0.20. : Enter the nslookup command, press Enter to enter the DNS resolution query interface. .

Step Four: enter the corresponding domain name which you can not access the site . If not accessible, then the DNS resolution can not working. We will receive the DNS request timed out, timeout was 2 seconds of the message. This shows that our computer is really on a DNS resolution failure.

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