Date: Mon, 3 May 1999 00:01:22 -0400 (EDT) From: "Crist J. Clark" <cjc@cc942873-a.ewndsr1.nj.home.com> To: gkshenaut@ucdavis.edu Cc: questions@FreeBSD.ORG Subject: Re: variable-sized subnets in class C Message-ID: <199905030401.AAA20254@cc942873-a.ewndsr1.nj.home.com> In-Reply-To: <199905030117.SAA16692@deal1.bogs.org> from Greg Shenaut at "May 2, 99 06:17:23 pm"
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Greg Shenaut wrote, > I am trying to divide up my class C network into variably sized > subnets. I think I understand how to do this, but I thought I'd > write up what I think to be the constraints, and see if anyone > more knowledgeable than I could keep me from making a mistake. [snip long explination] I think you have made this a lot more complicated than it really is. First, there is no real reason to limit the discussion of this to class C subnets. We could equally well talk about 20-bit nets or any mask with less than three bytes. Second, you do have one thing wrong. > The rules are: the highest and lowest address in each network cannot > appear in a subnet. It is a misconception that the lowest subnet and highest subnet are unuasable. According to RFC 1812 subnets of all zeros or all ones are legal and should be supported by all routers (only the _very_ oldest of routers may not comply). With this in mind, you can cut up a C class pretty much any way you want. Think of it this way, you can take it and cut it in two for two 128 member (126 usable of course) nets. Each if those can (but do not need to be) cut in two again, and any results from that can be cut down again, etc. etc. until as you pointed out, you reach a 4 member net, the smallest that can have "real" hosts. -- Crist J. Clark cjclark@home.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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