A NethServer system is constituted by RPMs that come mainly from CentOS mirrors and NethServer mirrors.
- CentOS releases errata and bugfixes recompiling RHEL packages, as reported by the centos-announce mailing list.
- NethServer does the same, announcing new releases of its specific RPMs on http://dev.nethserver.org
All those packages updates improve the original system release by pushing it forward, like rolling continuously.
When CentOS produces a new minor version like 6.7 they publish a new “minimal” ISO image. The NethServer developers add a small RPM set on that image together with a kickstart file. The resulting image is the NethServer ISO, with installer, server-manager and other stuff.
When NethServer 6.7 is released, any existing 6.6 installation can be upgraded seamlessly, because both CentOS and NethServer ensure compatibility between minor releases.
NethServer mirrors host also some RPMs from other sources, like EPEL, RepoForge… Those packages are updated only after successful tests as tracked on dev.nethserver.org.