Is it possible to have no entries in "Search Domains:", which is located under the DNS tab if Network of System Preferences?
I'm trying to solve the problem of having Windows computers connect with my Mac, and getting help in this effort from Microsoft forums. My Mac has no problems in connecting to the Windows systems.
There is no requirements to have a search domain. They are just there to allow you to not need to enter the entire name name.
For example: If you have a search doman for MyCompany.com, then you can if you have a hostname such as Fred.MyComputer.com, you can just enter "Fred", and the search domain will automatically provide the MyCompany.com
But you are welcome to enter the full domain name.
If the [-] does not become active when you select a search domain, then it is possible your DHCP server has provided the search domain, and it is not in your control. BUT, you should be able to enter your own search domain, and that should that priority.
An unremovable (but replaceable) search domain is usually passed along by the router from the ISP/modem, if separate .
Here on Sierra, at least, and I'm sure earlier versions too, tcpdump is included with macOS.
You'll need to use Terminal, and your admin password, and copy/paste a command, then either renew DHCP or power off/on wifi.
sudo tcpdump -i en0 -vv | grep Domain-Name
copy the entire text above, then paste it into Terminal, while using your Mac in an admin user account
press enter/return : you'll be prompted for your admin password. Type it in, followed by enter/return; it won't be echoed on the screen. You can expect an initial output similar to below
tcpdump: listening on en0, link-type EN10MB (Ethernet)
Now power wifi off/on or renew DHCP lease & here, anyway, I see this after a few seconds :
Subnet-Mask, Classless-Static-Route, Default-Gateway, Domain-Name-Server Domain-Name, Option 119, Option 252, LDAP Subnet-Mask, Classless-Static-Route, Default-Gateway, Domain-Name-Server Domain-Name, Option 119, Option 252, LDAP Domain-Name-Server Option 6, length 4: 10.0.1.1 Domain-Name Option 15, length 20: "hsd1.nh.comcast.net."
After say 10 seconds, or if you see a similar output; quit tcpdump in Terminal by using ctrl c
Here anyway, the relevant line is 'Domain-Name Option 15' but it should be obvious because your search domain ought to be there, in quotes.
Mine's forced by the ISP via a cable modem, then AirPort Extreme. No menus to clear/alter it that I have ever seen.
Clear search domains in network preferences
