In iOS Wifi settings, each Wifi connection has a Search Domains section, usually blank.
What is this used for?
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A Search Domain is simply a convenience that allows the system to convert host names to Fully Qualified Domain Names (FQDN). Anyplace you might use a FQDN, such as in the location bar of Safari or as an argument to
ssh, you can use a simple host name. If the system can resolve that host name to an IP address (e.g.
localhost -> 127.0.0.1) then it will use that. If that doesn't work, then the system will try appending the search domain to the host name and try again. If you specified more than one search domain, it will try them each in order.
If you are typically connecting to other Mac's on your LAN, then setting the search domain to
local will make it easier to use just the other computer's names everywhere. If you are in a corporate environment and all your servers are available at
name.example.com, then setting a search domain of
example.com will allow you to access them by just using
Those are the two most typical use cases. When using a public Wi-Fi network, you should leave the Search Domain blank/empty to avoid accidentally connecting to some computer you didn't mean to connect to.
A search domain is a way to adjust the domain when looking up an address. As in, assist in defining the actual domain name, only having to use part of it in a local network.
For example, in some networks, the Search Domain '.local' may be used to append to what a user puts into their URL bar in their browser, like a user can just type 'intranet', but it knows to complete this to 'intranet.local'.
Some routers do something similar to help devices find each other on a local network.
In many cases, this is set by your network gear, similar to acquiring an IP address through DHCP.
Same as in OS X when you look in the "Network" System Preference. LINK