When running the Xilinx Information Center and prompted for User ID and password login seems to work.
The Xilinx Unified Installer is downloaded and runs and prompts me to change proxy settings.
I set these to the settings that I have in other apps, click Test Connection, and it always fails.
The only thing I can think that can cause this is that the Authentication Service you use in the Xilinx Unified Installer is not the same as the Xilinx Information Center, and the company firewall is blocking this.
If this is the case can you send details of the Authentication Service for the Xilinx Unified Installer so that I can put in a request to allow access through the company firewall.