Docker swarm node not able to pull image from private registry

we want to setup private registry to host our own application images.
If a repository having public access we could create a services using docker service command but when we change it to private we can not run docker service command eventhough given full access to repo wrt user.
Currently we are using Docker version 1.12.6, build ec8512b/1.12.6 & OS Version: RHEL 7.4 (Maipo)