Ivan Adams wrote:
My goal is using more bandwidth with apt-proxy servers on my friends, who have other internet connection. And I want to download first packet from my internet and second packet at the same time from the apt-proxy with my friend internet connection. Now, I can only download all packets from my internet, and if it fails will go to the apt-proxy ...
Sounds like your /etc/apt/sources.list does not match your expectations. Servers will be used in the order they appear in the file.