Can I create an outage that includes all devices, at the present time due to a firewall issue we have to reload it at a certain time on a weekly basis, this causes a loss of communication to some devices. Is there a default group that I can use when I set a weekly outage that includes all devices or do I have to name all devices explicitly.
yes, that's possible in versions 8.6.1 and newer, but only using the command line tool /usr/local/nmis8/admin/outage_admin.pl: the GUI for setting up outages doesn't expose all options.
simply start ./admin/outage_admin.pl act=create for an explanation of the possible options, and select your nodes with a sure-fire regexp like "/.*/".