RFC关于非连续子网掩码的小说明

 在RFC 950 - Internet Standard Subnetting Procedure中有一小句这样子的声明：

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Since the bits that identify the subnet are specified by a bitmask, they need not be adjacent in the address. However, we recommend that the subnet bits be contiguous and located as the most significant bits of the local address.

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然后在RFC 1219 - On the assignment of subnet numbers对RFC 950其中的子网号设定作了一些补充，在这里就可以看到对RFC 950的一些总结：

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RFC-950 [2] specifies a procedure for subnetting Internet addresses using a bit-mask.  While RFC-950 allows the "ones" in the subnet mask to be non-contiguous, RFC-950 recommends that 1) they be contiguous, and 2) that they occupy the most significant bits of the "host" part of the internet address.

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在其中就可以看到RFC并不要求子网掩码必须是连续为1的，即允许为非连续子网掩码，不过并不推荐这样做。但是在大多数系统中，尤其是Windows系统中，以Windows XP为例，如果设定非连续子网掩码的话，将会出现如下提示：

不知这个能不能在Windows XP的系统说明里面能不能找到，期待ing...