我知道以下类型的 Vlan。

Default VLAN: This is basically where ALL ports belongs to by default, this is technically VLAN 1 and it can't be deleted from the switch. 

Data VLAN: 

Native VLAN: The native VLAN is an 802.1Q only concept. 

Voice VLAN: The voice VLAN is where the QoS policies are applied in order to prioritize this traffic to send it through the LAN. 

Management VLAN: This is used on a LAN for management purporses. 

Special VLANs: These VLANs are basically used for special cases on your LAN. 

Reserved VLANs: There are some VLANs that are reserved internally on your switch in order to use them on other enviroments like FDDI, Token Ring.

Private VLANs it's a technology that has some new concpets/category of VLANs.

但最近在戴尔电源连接开关中，我看到 Vlan 类型是永久的。谁能告诉我永久vlan类型是什么意思。