DNS Forwarders

Now that we have prompted our domain controller, we need to configure DNS forwarders to help with external name resolution.  Thus far, internal name resolution will be handled by our domain controller/DNS server but how do we handle the Internet?

The answer is simple, we configure a DNS forwarder on our DNS server.  DNS forwarders forward queries for unknown domains to other DNS servers for name resolution and cache their responses based on the TTL (time to live) value set with the associated record.

So in other words, if our DNS server doesn't know the address for say, www.google.com, then it will ask a downstream DNS sever (a forwarder) if it knows the address.  The downstream DNS server intern performs the same lookup and forward the query on if it doesn't know the address for the host.  This process repeats itself until your query either hits a DNS server with a cached response (the TTL hasn't expired for the record) or your query finds its way to the SOA (start of authority.)  The answer is then returned along the same path with a TTL value so that it may be cached for quicker subsequent look-ups.

Typically you will set your DNS forwarders to your ISP's DNS server(s).  Your ISP should provide you with the address(s) for their public DNS servers.  In the following example, we will set our DNS servers to TCPDump's ISP's DNS servers, but you should make certain to replace the address from our example with your ISP's DNS servers as you'll most likely not have access to query our servers.

1. Log on to the new domain as the domain administrator.  Ensure you select the domain from the Log on to menu drop down
   
   
   Note: The NetBIOS name you chose from the dcpromo command should be listed in the "Log on to" menu drop down
   
   
2. Run the DNS management snap-in (Start -> Run -> dnsmgmt.msc)
   
   
   
   
3. Right click on the hostname of your server and select Properties
   
   
   
   
4. From the Forwarders menu, add your ISP's DNS servers
   
   
   Note: The addresses shown above are TCPDump's ISP's DNS servers.  You should set this to your ISP's DNS servers
   
   
5. Apply the change and close the DNS properties window
   
   
6. Verify DNS functionality querying for your domain controller and a external site like www.google.com
   
   

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Baskaran |07/08/2010 20:59:34 please give guidlines to know about virtual machine Reply | Quote

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