How do you get to your critical systems if the network is down? There are a number of different technologies that are used in this case. Often, they involve some kind of terminal server that is connected to the system via a serial terminal (yes… there are still some of them around), or via an IP based KVM switch. The terminal server itself may be reachable via a backup network connection, or maybe someone even has a dial-in setup around for them. But no matter the exact technology you are using to implement this, a “backup connection”, or “out of band connection” often bypasses a lot of security controls. This is done by design to ensure that the backup connection can be used even if these security devices do not respond. Often, these connections are also used to manage security devices.
Article Link: https://isc.sans.edu/diary/rss/22894