DHCP-supplied DNS servers are not removable

When users connect to networks with a DHCP server such as those most home routers contain, they are provided with automatic configuration settings that include the essential IP address, network mask, and gateway. In addition, users are supplied with a DNS server to resolve hostnames to their respective IP addresses so users can access web resources by name instead of having to enter IP addresses.

For some users the automatically supplied DNS server provided by their ISP does not adequately meet their needs, and users might wish to use their own DNS servers. The problem these users face is that the automatically assigned DNS server entries in OS X are not editable, and therefore cannot be removed in place of another server. While users can add additional entries to the DNS server list, the initially assigned server remains active and at the top of the list. OS X does address user-defined DNS servers with priority over the automatically supplied one, but there is a chance that other DNS servers may be unreachable so the default one gets accessed. In addition, some users may just wish to have manually entered addresses and avoid automatic configurations altogether.

To disable OS X's automatic configuration for DNS server settings, users must edit the "IPConfiguration.xml" system file using the following procedure:

1. Open the Terminal and enter the following command (copy and paste if necessary):

• sudo pico /System/Library/SystemConfiguration/IPConfiguration.bundle/Contents/Resources/IPConfiguration.xml

Enter the administrator password when prompted and the configuration file will open in a terminal text editor.

2. Using the arrow keys, scroll down to where the following text appears (about half-way down the file):

• DHCPRequestedParameterList
• 1
• 3
• 6
• 15
• 119
• 95
• 252
• 44
• 46
• 47

3. Remove the full lines containing the "6", "15", and "119" entries, so the whole array looks as such:

• DHCPRequestedParameterList
• 1
• 3
• 95
• 252
• 44
• 46
• 47

4. Press "ctrl-o" followed by "enter" and "y" to confirm saving the file.

5. Press "ctrl-x" to save the file.

6. Quit terminal and restart the computer. The DNS server list should now only accept manually entered servers.

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