The HighSide client requires connections to three servers over TCP port 443. These servers are

  1. highside.io 
  2. relayproduction.Highside.io
  3. maps.googleapis.com.

These servers do not have static IP's.

*Note* Google Maps is only used when admins are creating location restrictions for a user group, Google Maps is not used anywhere else

Also note that HighSide uses a self signed certificate so if your network has self signed certificates block you may need to file for an exception to use HighSide.