136 lines
4.8 KiB
HTML
136 lines
4.8 KiB
HTML
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<TITLE>The Answer Gang 83: Homework question: defining subnets</TITLE>
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<H3 align="left"><img src="../../gx/dennis/qbubble.gif"
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height="50" width="60" alt="(?) " border="0"
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>Homework question: defining subnets</H3>
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<p><strong>From Darren Collins
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</strong></p>
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<p align="right"><strong>Answered By Faber Fedor, Frank Rodolf, Jim Dennis
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</strong></p>
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<P><STRONG>
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How do you specify the first 6 & last 2 available subnets defined by the
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IP address and subnet mask (155.25.0.0/23) Any help on this would be
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greatly appreciated.
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</STRONG></P>
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<P><STRONG>
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Sincerly, Darren
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</STRONG></P>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Faber]
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How do I? Very well, actually. I usually use a calculator, but using
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an abacus is much more challenging!
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</blockQuote>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Frank]
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But doing it by hand is more fun!
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</blockQuote>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Faber]
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Have you looked here <A HREF="http://www.learntosubnet.com"
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>http://www.learntosubnet.com</A> ?
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</blockQuote>
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<blockQuote>
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BTW, we don't do homework assignments around here, except for our own,
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of course.
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</blockQuote>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [JimD]
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The reason we know it's a homework assignment is because no one uses
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this scheme in the real world. This would define 126 subnets of
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510 hosts each (or 128 subnets --- with modern equipment). The first
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subnets would be 155.25.0.* <EM>AND</EM> 155.25.1.*; the next would be
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.2.* and .3.*; etc.
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</blockQuote>
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<blockQuote>
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This is a bit-aggregation (supernetting) over the traditional "class
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C" sized network. Normally people would go for a 4-bit aggregation
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--- giving them 16 networks of about 4000 hosts each (and possibly
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fanning those into class C sized networks through another hierarchical
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layer of routers).
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</blockQuote>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Frank]
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Actually, there are real world exceptions to the 4-bit aggregation.
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The multinational I am working at nowadays uses a 21-bit mask on a lot
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of sites. (And it still has me confused at times.)
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</blockQuote>
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<h5>
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<br>Copyright © 2002
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<br>Copying license <A HREF="">http://www.linuxgazette.com/copying.html</A>
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<BR>Published in Issue 83 of <i>Linux Gazette</i>, October 2002</H5>
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