When do I use nginx reverse proxy to proxy from an IPv4 network to an IPv6 network, I used the following configuration file:

upstream ipv6server {
server [2001:: 1];
server [2001:: 2];
}
location / {
proxy_pass http://ipv6server;
}

Nginx can start normally, but the start time, when I gave when the HTTP request, Nginx's CPU usage is particularly high, almost 100%, do not know why.

I think the current code should support Nginx of IPv4 to IPv6 proxy it, do not know how to configure for normal use it? Thank you.