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Which version to install depends on which version of MacOS you have. For OSX 10.7.5 and up we currently recommend the most recent stable release which may be downloaded from .

For older Macs version 3.5.25 should work which can be found here .

If you have difficulty with the version you downloaded and you're on OSX 10.7.5 or higher, then try the latest beta release from . For older versions of OSX there is no readily available alternative. 

After installing tunnelblick, download the config file. The configuration file is compressed, so double-click it to expand it: you should then get a file 'chemistry.tblk'. ('chemistry.tblk' will not run from the Downloads folder. Copy to the Desktop). Double-click 'chemistry.tblk' to install the configuration.


Select 'Connect Chemistry' from the TunnelBlick icon. The credentials you should use are your ChemNet credentials. These can be collected from and it is OK to tell Tunnelblick to save them. If you are using Chrome as your web browser please type the credentials in, do not cut and paste as this has been proved not to work. Please note that the ChemNet username is your CRSID followed by , not . 

Dealing with the warning: 'apparent public IP address was not different after connecting'

This warning appears when connecting using newer versions of Tunnelblick with our latest configuration files. It is a warning, not an error. It happens because in Chemistry and SPRI we configure the VPN to only send network traffic destined for the University of Cambridge over the VPN link, and all other traffic goes direct to its destination. This setup gives the best network performance for videoconferencing, while still allowing you to access University-only resources. There are two ways to avoid the warning:

  • Disable the IP address checking feature using the checkbox on the "Preferences" panel of Tunnelblick's "VPN Details" window.
  • Switch to using a 'Full Tunnel' configuration file. This will send all your network traffic via Chemistry's network when the VPN is on and may be slower. Full tunnel configuration can be downloaded from