Down indicates that a port or interface has failed or is in testing mode. A Down notification is generated when the port or interface is not physically connected. In addition, a Cable Down notification can encompass Router Down problems multiple hops away.
There are physical interfaces that underlie logical interfaces. These physical interfaces may not have a direct network connection associated with them, but the logical interfaces that are layered over those physical interfaces have a direct network connection. In such a scenario, if a physical interface goes down, it will be the root cause of network connections for logical interfaces going down. In this case, Interface Down will be the root cause and will have network connection alerts as its impact.
When a port or interface is physically connected, network adapter Down is superseded by a NetworkConnection Down diagnosis.
For ports, this means that Port Down is superseded by:
TrunkCable Down if the port is connected through a trunk cable.
Cable Down if the port is connected through a cable.
For interfaces, this means that Interface Down is superseded by:
NetworkConnection Down if the interface is connected through a physical network connection.
Cable Down if the interface is connected through a cable.
Notification of network adapter Down is controlled by the Testing Notification Mode threshold.
The events used to diagnose Down include:
System MightBeDown for any logically connected systems