<code>IgnoreUnknown</code> is there so this config will work with non-Apple ssh implementations. You do not need to use '''ssh-agent(1)''', or enable any special Apple-specific options for the ssh agent, ignore the Internet misinformation. Of course you can do this per-host, or per-key, but then <code>IgnoreUnknown</code> should come early in your configuration, before any use of <code> UseKeychain </code>.