Some devices have interfaces that are virtual interfaces. These are interfaces that exist inside the device, but don’t relate to a physical plug on the outside of the device.

A VLAN interface is an example of a virtual interface. Some devices have “loopback” interfaces. Typically, these interfaces are not valuable to monitor, as they don’t have any error counters or utilization information associated with them. Thus, they can be ignored.

Click Here more information on Ignoring Interfaces