what is the update servers ip range?

Hello all, we have a client with avast 4.7 running in 10 pcs. They updated always fine, but last week the client has installed a proxy server. The port 80 now is blocked to outside and the pcs can’t navigate, so avast can’t update. It’s possible to allow ip exceptions, but avast connect to a different ip every time it tries to update. Which ip range must I allow if we want avast to update successfully?

Thanks in advance

There is no IP range, our servers are connected to different providers, each using multiple ip ranges.

They may create user account on the proxy and setup avast updater to use the account to update.