How can I force default DNS query to work in TCP mode?

Solution 1:

AFAIK it's not possible to force the mDNSResponder to use TCP instead of UDP.

I've found a workaround though. The method outlined below uses a local DNS-proxy (dnschef) forced to use TCP for outgoing DNS-requests.

• Download and unzip dnschef-0.3.
• Download and unzip dnslib

• Download and unarchive IPy-0.76

• cd to the dnslib folder:

  cd ~/Downloads/paulc-dnslib-04713cc4a9df 
  

• install dnslib:

  sudo python ./setup.py install
  

• cd to the IPy folder:

  cd ~/Downloads/IPy-0.76 
  

• install IPy:

  sudo python ./setup.py install
  

• Open System Preferences -> Network, replace your current DNS-server(s) (e.g. 8.8.8.8/8.8.8.4) by a local one with the IP 127.0.0.1 and apply the changes.

• cd to the dnschef folder and start it:

  cd ~/Downloads/dnschef-0.3 
  sudo ./dnschef.py --nameservers 8.8.8.8#53#tcp
  

If the last command is too troublesome or ugly (well, it is ugly because you have to open Terminal.app and start the DNS-proxy), you can move the dnschef.py and .ini to another path and create a launch daemon to start the DNS-proxy while booting.

Example:

• sudo mkdir /usr/local/python
• sudo cp ~/Downloads/dnschef-0.3/dns* /usr/local/python/
• sudo rm /usr/local/python/dnschef.exe
• sudo touch /Library/LaunchDaemon/local.dnschef.plist

• copy and paste the following content into the newly created file with an appropriate editor
  (e.g sudo nano /Library/LaunchDaemon/local.dnschef.plist):

  <?xml version="1.0" encoding="UTF-8"?>
  <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
  <plist version="1.0">
  <dict>
      <key>Label</key>
      <string>local.dnschef</string>
      <key>ProgramArguments</key>
      <array>
          <string>/usr/local/python/dnschef.py</string>
          <string>--nameservers</string>
          <string>8.8.8.8#53#tcp</string>
      </array>
      <key>RunAtLoad</key>
      <true/>
  </dict>
  </plist>
  

• Load the file with sudo launchctl load -w /Library/LaunchDaemons/local.dnschef.plist

  All files and folders created must be owned by root:wheel.