What happens to packets when an interface on a Junos device is administratively down?

When an interface on a Junos device is administratively down, it is effectively taken out of service by the administrator. In this state, the interface does not participate in the forwarding of network traffic. Any packets that arrive at this interface will be discarded, as there is no active route for them to follow or any way for the device to process them further.

This behavior is crucial for network management, as it ensures that traffic is not inadvertently sent or processed in a way that could lead to misrouting or confusion in traffic management. Additionally, the administrative down state is used to take interfaces offline for maintenance or configuration changes without affecting other device operations or interfaces.