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Don Burleson Blog 









Resolving host names with DNS for Oracle

Don Burleson


With Oracle, the tnsnames.ora file allows you to connect directly to a database using the TNS "service name".  When an Oracle connection is requested, Oracle goes to the tnsnames.ora file and looks-up the service name entry in the tnsnames.ora file and gets:

1 - The host server name
2 - The protocol
3 - The port to use to connect to the server

But how does Oracle resolve the host name to an IP address.  In UNIX, special lookup files exist that pair the host name with the IP address.  Termed "Domain Name Services" (DNS), the DNS is especially useful because when a server changes an IP address, you only need to make the change in one place on the server and all host name connections will immediately find the new IP address.

Host name to IP address resolution files

UNIX /etc/hosts
Windows NT/2000/XP Pro c:\winnt\system32\drivers\etc\hosts or hosts.sam
Windows XP c:\windows\system32\drivers\etc\hosts or hosts.sam

In UNIX we vi the /etc/hosts file.  In Windows we open the hosts.sam file using Notepad.

Dynamic DNS resolution on UNIX/Linux

The /etc/hosts file contains the IP address, host name resolutions: chicago     toyoko

To use DNS on UNX/Linux, you need to ensure that the server is configured for DNS:

1.  the /etc/host.conf should have the line:

   order hosts,bind

2 - The /etc/nsswitch.conf should have this line:

   hosts: files nisplus nis dns


Dynamic DNS resolution on Windows

In Windows XP we use DHCP, Dynamic Host Configuration Protocol and this must be enables to use automatic host name resolution.

DHCP Configuration for Windows XP:

  1. Right click on "My Network Places" icon on your desktop or go to the "Start Menu", select "Control Panel", then select "Network Connections"
  2. Within the "Network Connection" window, double click on "Local Network Connection"
  3. Select "Properties"
  4. Select "Internet Protocol (TCP/IP)" within the connection items
  5. Click on the "Properties" button.
  6. Under the General tab, select "Obtain IP address automatically" and "Obtain DNS server address automatically"



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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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