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cidr [2016/05/09 16:22] steve |
cidr [2016/05/09 16:35] steve |
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| That is, if you have ''192.168.1.0/21'', which gives you ''8'', then if you go down one # -- from ''192.168.1.0/21'' to ''192.168.1.0/20'' -- 20 being the next possible range size, then your number ''8'' is going to double to ''16''. | That is, if you have ''192.168.1.0/21'', which gives you ''8'', then if you go down one # -- from ''192.168.1.0/21'' to ''192.168.1.0/20'' -- 20 being the next possible range size, then your number ''8'' is going to double to ''16''. | ||
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| + | The opposite is also true, going from ''192.168.1.0/21'' to ''192.168.1.0/22'' is going to give you less addresess -- 4. | ||
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| + | The reason this can get confusing, trying to keep track of which numbers are higher or lower, remember that the higher the number on the CIDR, the lower the amount of possible IPs. Instinct may tell you that ''/32'' is higher than ''/24'' and so a ''/32'' notation means more. The opposite is true. It's like a see-saw! Only one can be high. | ||
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| + | <code> | ||
| + | 192.168.1.0/32 - the notation is high, so the IPs is low | ||
| + | 192.168.1.0/16 - the notation is low, so the IPs is high | ||
| + | </code> | ||
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| + | The power of ''2'' is also evident when crossing the first 256 # of IP addresses. If starting at ''192.168.1.0'', and extending to ''512'', then you're only adding one set of ''256''s. So ''1.0'' would expand to ''2.0''. But what if you wanted to add more? The power of 2 applies, so you'd then have to jump by ''4'', next. ''192.168.1.0'' now goes to ''192.168.4.0''. The next one would be ''4'' times ''2'', so 8 is the next possible block. Going from ''192.168.1.0'' to ''192.168.8.0''. | ||
