技术上说，VPN是指将物理上分布在不同地点的网络，通过公用骨干网连接而形成的逻辑上的虚拟子网。
In technology, VPN means the networks locating in the different places are connected by main public networks, which shape the logic networks.
在 Linux 和 Solaris 系统上，可以在一块物理以太网卡上创建多个虚拟接口，让它们连接到不同子网上的 IP 地址。
On both Linux and Solaris, you can create multiple virtual interfaces to IP addresses on different subnets on one physical ethernet card.
如果可以使用虚拟LAN (VLAN)中继，就可以通过同一个物理适配器同时访问多个子网，但是这种方法无法享有这一好处。
If virtual LAN (VLAN) trunking is available, where multiple network subnets can be accessed simultaneously through the same physical adapter, this method does not use that benefit.
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