DNS Troubleshooting


There are many reasons why a domain name may not be resolving to the server (i.e. when people enter the domain, they do not arrive at the correct server). This guide covers typical reasons, and how to overcome them, as well as give a simplified explanation of how DNS works.

Note: If the name servers have recently been changed, this means the changes need to propagate. However, always check the settings to make sure that it is setup as you expect. Just because the name servers were recently changed, does not mean they were changed correctly.

If it appears there is a problem with the DNS, you can check to following.

  • First check and make sure that the name servers are correct. You can view the current name servers at a variety of places, including http://intodns.com and http://www.internic.net/whois.html. You can view the correct (expected) name servers in a variety of places, including the new account e-mail, and the cPanel for shared web hosting accounts (or SuperTool for employees).
 http://support.hostgator.com/articles/hosting-guide/lets-get-started/dns-name-servers/what-are-my-name-servers
  • Make sure the domain is registered and not expired; this also can be checked in whois. If the domain is expired, it will need to be renewed. If it is not registered, it will need to be registered. 
http://support.hostgator.com/articles/hosting-guide/how-to-buy/domain-names/how-do-i-renew-my-domain-name
  • DNS Glue (Name Server Records Not Listed in DNS Properly). For reseller accounts, VPS, and dedicated servers, it is possible that the name servers are not properly added to the DNS Zone. You can check by going to http://intodns.com and seeing if it reports “No Glue” next to the name servers listed. If so, follow the directions here:
 http://support.hostgator.com/articles/hosting-guide/lets-get-started/dns-name-servers/dns-glue
  • Make sure the A Records Point to the Correct IP. Although most of the time this will be correct if cPanel configures it automatically, there are a number of reasons why this could be be incorrect. This sometimes happens when you are not using our name servers, or if you manually made changes to the DNS zones.
 http://support.hostgator.com/articles/cpanel/how-to-change-dns-zones-mx-cname-and-a-records
    DNS

    DNS

    Propagation

    When you make certain changes to the DNS, such as name server changes, “A” record changes, “MX” record changes, etc., it takes time for those changes to propagate (or update) worldwide. Some people will see the change instantly and some will see the change within up to 48 hours (depending on what was changed).

    What is Propagation and Why Does it Take so Long?

    The reason why propagation takes so long is because computers cache (remember) the old setting for a period of time. What is happening is that your computer, as well as servers on the internet, only check for DNS changes every so often. They typically do not check to see if the settings have changed every time you make a request. It assumes it is the same as the last time it checked. For name server changes, your computer and servers on the internet will cache this information for up to 48 hours. For other changes, such as A Records, MX Records, CNAME Records, etc., it will remember the old settings for up to 4 to 8 hours before checking to see if the settings have changed.

    But Can I See My Site before it Propagates?

    You can see your site sooner by viewing the site via an alternate URL. Read more at http://support.hostgator.com/articles/hosting-guide/lets-get-started/dns-name-servers/how-can-my-clients-view-their-site-before-the-dns-has-propagated

    But Can I See it Sooner with the Domain Name?

    If you cannot see your site after changing the name servers due to propagation, it may be because your computer is remembering the old name server settings. You may be able to see your site sooner by flushing the DNS on your computer (assuming your internet service provider is not also caching the DNS). You can follow the directions below to accomplish this.

    Flush DNS

    http://support.hostgator.com/articles/hosting-guide/lets-get-started/dns-name-servers/flush-dns

    If flushing the DNS does not work, then either the name servers have not been updated, or your internet service provider (ISP) is caching the DNS. If your ISP is caching the DNS, you will have to wait until propagation finishes to view your site via your domain name. This can take up to 48 hours.

    If that does not work, there is a more technical way to make sure you can see your site sooner, by temporarily changing your hosts file on your computer. This will force your computer to go to our server’s IP address for the most recent information. This does not actually fix the DNS; rather, it lets you see the site with your domain name, regardless of what the DNS says.

    Modifying the Hosts File

    http://support.hostgator.com/articles/specialized-help/technical/how-do-i-change-my-hosts-file

sumber : http://support.hostgator.com/articles/hosting-guide/lets-get-started/dns-name-servers/dns-troubleshooting-guide

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