Juniper Exam JN0-649 Topic 5 Question 55 Discussion

The forbidden mode does not register or declare VLANs. You can change the registration mode of a specific interface to forbidden. An interface in forbidden registration mode does not participate in MVRP even if MVRP is enabled on the switch.

https://www.juniper.net/documentation/us/en/software/junos/multicast-l2/topics/topic-map/mvrp.html

MVRP is disabled by default on the switches and, when enabled, affects only trunk interfaces. Once you enable MVRP, all VLAN interfaces on the switch belong to MVRP (the default normal registration mode) and those interfaces accept PDU messages and send their own PDU messages. forbidden---The interface does not register or declare VLANS (except statically configured VLANs).