Console Port Overview
Console ports allow access to Junos OS devices, regardless of the state of the Junos OS device, unless it is completely powered off. By connecting to the console port, you can access the root level of the Junos OS device without using the network to which the device might or might not be connected.
A console connection provides persistent direct access to a device that can often be accessed even when the primary network has failed.
We recommend that you perform all Junos OS and software package upgrades using the console because this connection will always remain up for the duration of the upgrade, enabling you to monitor status and progress. Other network-based connections such as SSH or telnet are often interrupted during software upgrades, which can cause status or error messages to be missed.
See the hardware guide for your particular Junos OS device for instructions on how to connect to the console port.