Deleted com.apple.mDNSResponder.plist in Mavericks, how to get it back?
Here is the contents of my /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist from OS X 10.9.1:

&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"&gt;
&lt;plist version="1.0"&gt;
&lt;dict&gt;
    &lt;key&gt;Label&lt;/key&gt;
    &lt;string&gt;com.apple.mDNSResponder&lt;/string&gt;
    &lt;key&gt;OnDemand&lt;/key&gt;
    &lt;false/&gt;
    &lt;key&gt;InitGroups&lt;/key&gt;
    &lt;false/&gt;
    &lt;key&gt;UserName&lt;/key&gt;
    &lt;string&gt;_mdnsresponder&lt;/string&gt;
    &lt;key&gt;GroupName&lt;/key&gt;
    &lt;string&gt;_mdnsresponder&lt;/string&gt;
    &lt;key&gt;ProgramArguments&lt;/key&gt;
    &lt;array&gt;
        &lt;string&gt;/usr/sbin/mDNSResponder&lt;/string&gt;
    &lt;/array&gt;
    &lt;key&gt;MachServices&lt;/key&gt;
    &lt;dict&gt;
        &lt;key&gt;com.apple.mDNSResponder&lt;/key&gt;
        &lt;true/&gt;
               &lt;key&gt;com.apple.mDNSResponder.dnsproxy&lt;/key&gt;
               &lt;true/&gt;
    &lt;/dict&gt;
    &lt;key&gt;Sockets&lt;/key&gt;
    &lt;dict&gt;
        &lt;key&gt;Listeners&lt;/key&gt;
        &lt;dict&gt;
            &lt;key&gt;SockFamily&lt;/key&gt;
            &lt;string&gt;Unix&lt;/string&gt;
            &lt;key&gt;SockPathName&lt;/key&gt;
            &lt;string&gt;/var/run/mDNSResponder&lt;/string&gt;
            &lt;key&gt;SockPathMode&lt;/key&gt;
            &lt;integer&gt;438&lt;/integer&gt;
        &lt;/dict&gt;
    &lt;/dict&gt;
    &lt;key&gt;EnableTransactions&lt;/key&gt;
    &lt;true/&gt;
    &lt;key&gt;BeginTransactionAtShutdown&lt;/key&gt;
    &lt;true/&gt;
    &lt;key&gt;POSIXSpawnType&lt;/key&gt;
    &lt;string&gt;Interactive&lt;/string&gt;
&lt;/dict&gt;
&lt;/plist&gt;


It'd probably be worth running a permissions repair after restoring the file.