I set forward proxy server using apache mod_proxy, which connects to 20 other proxy servers using ProxyRemote feature.
You can set just one URL for ProxyRemote , in my case it's proxy.mydomain.com:8085
I set round-robin for this subdomain with 20 different proxy IP addresses. nslookup and ping proves that round-robin works properly.
When I use this setup ProxyRemote is using only machine from the closest subnet to its IP.
So for example if my machine is 91.123.123.123
and my proxies are
5.4.12.9
188.23.9.111
91.222.111.99
and so on...
it always uses 91.222.111.99 and never the others.
I have no idea why this happens and I really need one proxy machine which uses other 20 proxies.
The idea is to create one proxy machine which connects to the target URL with random IP everytime.