Using GitLab to manage existing git repos


I have a git server on my isolated network and would like to continue to use it to host my repos. I have gitlab hosted on another server (different machine connected to the same network) and would like gitlab to manage the repos hosted on the git server. Can I configure gitlab to connect to the git server instead of using a local directory for its repos? Alternatively, if gitlab would perform better using a clone of the git server’s repo in its local directory, can I connect the two so they are mirrors of one another? So if a push is made in gitlab (or to the gitlab repo) it will perform a push to the repo on the git server?