I will be upgrading the IOS on our Core Router (Cisco 6905) at 5:00am tomorrow morning (Tuesday Feb 8th).
The upgrade is to enable a new 10GB interface slot card.
All preparations are already in place, so I expect the downtimes to be short (5-10min each) and intermittent between 5:00-6:00am.
During the downtimes, all inter network-connectivity will be disabled. There will be no access to any services or resources during this time.
This will include but not limited to: email, internet, databases, VPN, etc.