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lucy24 - 3:39 am on Jan 12, 2013 (gmt 0)

:: drifting o/t ::

I was trying to think of an analogy for the 123.123.0.0/16 * notation and the closest I could come is this:

Suppose your personnel department's computer refuses to accept blank spaces, so there's no such thing as a five-figure salary. Any gaps have to be filled with leading zeros, like \$052,986 or \$098,250. Or \$000,060 for that guy who came in one day to change a few lightbulbs when the janitor was off. (Let's, uhm, assume for the sake of discussion that if you take home more than \$999,999 a year, the extra is not on your paycheck but somewhere else.)

Now you've got:

050,000/2 = first two digits have to be the same, so anyone whose paycheck is in the range \$50,000 through \$59,000.
050,000/3 = anyone in the range \$50,000 through 50,999.
050,000/4 = now you're in the range where you can compare paychecks without making anyone mad, since the difference is at most \$99.

050,000/1 = anyone who makes less than \$100,000, whether it's the \$50 lightbulb guy or the \$098,000 management trainee. In fact the 5 in second place is meaningless; the correct form becomes 000,000/1.

The dots in your CIDR ranges aren't decimal points. They're equivalent to the commas separating thousands in big numbers. Come to think of it, this is where non-English speaking people say "And your point is...?" or possibly "Huh what?" depending on how much contact they've had with big numbers in English-language texts. In binary-speak:

123
= 0 + 64 + 32 + 16 + 8 + 0 + 2 + 1
= 01111011
and so
123.123.0.0
= 01111011.01111011.00000000.00000000
= 01111011011110110000000000000000

... and you never need to stop and calculate what that final monster (123 x 2^24 + 123 x 2^16 + 0 etc.) would be in base ten. (I get two billion and something-- but I didn't pay much attention to the calculator so this may be entirely wrong.)

I could go on, but I suspect we are both getting tired.

* I first typed "123.456.0.0/78" but couldn't do it, even as a meaningless example.