Nagios Enterprises maintains repositories for RPM based Nagios XI installations and RPM and DEB packages for our cross platform monitoring agent, NCPA.
Our newest GPG Public Key - GPG-KEY-NAGIOS-V3
If you're running in an offline environment you have two choices for how to install Nagios XI. You can either clone the nagios and nagiosxi-deps repositories provided for CentOS and RHEL or download the offline tarball.
If you need help with these repositories, check out the Knowledgebase and Support Forum.