What is the "Search Domains" field for in the tcp/ip DNS settings control panel/preference pane for?

Solution 1:

These are for the mechanism for going from a machine name to a Fully Qualified Domain Name.

DNS searches can only look at a Fully Qualified Domain Name, such as mymachine.example.com. But, it's a pain to type out mymachine.example.com, you want to be able to just type mymachine.

Using Search Domains is the mechanism to do this. If you type a name that does not end with a period, it knows it needs to add the search domains for the lookup. So, lets say your Search Domains list was: example.org, example.com

mymachine

would try first mymachine.example.org, not find it, then try mymachine.example.com, found it, now done.

mymachine.example.com

would try mymachine.example.com.example.org (remember, it doesn't end with a period, still adds domains), fail, then mymachine.example.com.example.com, not find it, fall back to mymachine.example.com, found it, now done

mymachine.example.com. Ends with a period, no searching, just do mymachine.example.com

Soooo.....

If you have your own DNS domain such as example.com, put it there. If not, ignore it. It really is more corporate than a home setting.

Solution 2:

When searching for a computer name like "MyMac", you need to know the fully-qualified name of that computer. It might just be MyMac., or it might be something like MyMac.example.edu, or (in a business) MyMac.example.com. The search domains are how the system translates the short name to the full name.

This should be set per-connection, rather than once for your machine, because you may have something like a normal connection active at the same time as a VPN connection to your company, where traffic sent over the VPN should use a different search domain.