Ipv6 only host can not been connected in fetch()

In webbrowser development environment, if fetch() to an ipv6 only host, we got “502 Bad Gateway”, and “connect(): Network is unreachable” in error.

When in production environment, if fetch() to an ipv6 only host, we could get an “Error 521” page, and the error page show “host error”.

It seems that this issue has been reported for a long time, but not solved untill now.
Hope for a solution, many thanks.

sorry, it seems that this issue continues.
If the host has only ipv6 address, the fetch() returns “Network is unreachable”