The VLAN ID of the secondary VLAN configured on this
private port. A private port is a port that allows
the ingress traffic of the secondary VLAN as well as
egress traffic of its associated primary VLAN, but
blocks the egress traffic of the isolated VLAN while
allowing the egress traffic of the community
or twoWayCommunity VLAN depending on the type of the
secondary VLAN.
Note that a port can join a secondary VLAN only after
this secondary VLAN has been associated with a primary
VLAN, i.e., the cpvlanVlanAssociatedPrimaryVlan has a
non-zero value. The default value of 0 for this object
means this port has not joined any secondary VLAN yet.