Docker registry behind a proxy - mirror mode

Dear Docker Community,

I try to configure an internal docker registry to cache images.

We have a common network infrastructure with an anwfull proxy. registry → proxy → internet

I configure my docker daemon to use the proxy by specifying in :/etc/sysconfig/docker HTTP_PROXY and HTTPS_PROXY. Pulling image is working on this server.

But the registry complains when i try to set up the mirror mode :
panic: Get https://registry-1.docker.io/v2/: dial tcp: lookup registry-1.docker.io on [::1]:53: read udp [::1]:57502->[::1]:53: read: connection refused

it seems to be a network issue, but i don’t know how to handle it.
Could you please provide a tip ?