扫描类型有被动，主动，后者是用户自定义。

The type of scanning can be passive, active or user-directed.

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默认情况下，优化器考虑这种类型的扫描。

By default, the optimizer considers this type of scan.

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其他类型的扫描还包括，实际查看在网络中传输的原始数据包所包含的信息。

The other type of scanning involves actually looking at the information contained within the raw packets that go past on your network.

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