The standby interface in an IPMP group is not used for data traffic unless some other interface in the group fails. When a failure occurs, the data addresses on the failed interface migrate to the standby interface. Then, the standby interface is treated the same as other active interfaces until the failed interface is repaired. Some failovers might not choose a standby interface. Instead, these failovers might choose an active interface with fewer data addresses that are configured as UP than the standby interface.
You should configure only test addresses on a standby interface. IPMP does not permit you to add a data address to an interface that is configured through the ifconfig command as standby. Any attempt to create this type of configuration will fail. Similarly, if you configure as standby an interface that already has data addresses, these addresses automatically fail over to another interface in the IPMP group. Due to these restrictions, you must use the ifconfig command to mark any test addresses as deprecated and -failover prior to setting the interface as standby. To configure standby interfaces, refer to How to Configure a Standby Interface for an IPMP Group.