DOINC / Connected Cache and Proxy

I'm trying to get Connected Cache (DOINC) to work on our 1906 environment, but the installation of the service will not finish according to distmgr.log.

As far as I can tell from DoincSetup.log, it stops at requesting the test GIF file from the internet.

("requesting content from the delivery imitation in-network cache (DOINC) instance.")

This environment requires the use of a proxy server, for accessing the internet.

It does not require authentication, just that the traffic goes through the proxy.

I have tried adding (and verifying) the proxy in IE in System context using Psexec.exe -i -s, but no change.

I have tried adding the proxy in web.config (defaultProxy) on the CacheNodeService (and Default website) website in IE, but this doesn't seem to help. Also the information is removed again, every time DOINC setup runs again, so it seems like a loop at the moment.

How can I specify a web proxy for DOINC to use?

-Heine