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(tye)Re: converting complex netrange to cidr notation

by tye (Cardinal)
on May 11, 2001 at 13:33 UTC ( #79663=note: print w/ replies, xml ) Need Help??


in reply to converting complex netrange to cidr notation

Interesting problem.

#!/usr/bin/perl -w use strict; sub output { my( $nLow, $cBits )= @_; my $ipLow= join ".", unpack "C*", pack "N", $nLow; print " $ipLow/$cBits\n"; } while( <DATA> ) { my( $ipMin, $ipMax )= split " ", $_; print "$ipMin - $ipMax:\n"; my $nMin= unpack "N", pack "C*", split /\./, $ipMin; my $nMax= unpack "N", pack "C*", split /\./, $ipMax; my $bitsMin= 1; my $maskMin= 1; my $bitsMax= 1; my $maskMax= 1; while( 1 ) { while( 0 == ( $nMin & $maskMin ) ) { ( $maskMin <<= 1 ) |= 1; $bitsMin++; } last if $nMax < ( $nMin | $maskMin ); output( $nMin, $bitsMin-1 ); ( $nMin |= $maskMin ) += 1; } while( 1 ) { while( $maskMax == ( $nMax & $maskMax ) ) { ( $maskMax <<= 1 ) |= 1; $bitsMax++; } $nMax &= ~$maskMax; last if $nMax < $nMin; output( $nMax--, $bitsMax-1 ); } } __END__ 192.168.0.0 192.168.255.255 192.168.1.17 192.168.112.26
produces:
192.168.0.0 - 192.168.255.255: 192.168.0.0/16 192.168.1.17 - 192.168.112.26: 192.168.1.17/0 192.168.1.18/1 192.168.1.20/2 192.168.1.24/3 192.168.1.32/5 192.168.1.64/6 192.168.1.128/7 192.168.2.0/9 192.168.4.0/10 192.168.8.0/11 192.168.16.0/12 192.168.32.0/13 192.168.112.26/0 192.168.112.24/1 192.168.112.16/3 192.168.112.0/4 192.168.96.0/12 192.168.64.0/13
Sorry about the last half being output in the reverse order.

I haven't tested it extensively, but it feels right and works for the cases I did test.

        - tye (but my friends call me "Tye")


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Re: (tye)Re: converting complex netrange to cidr notation
by dino (Sexton) on May 11, 2001 at 15:07 UTC
    Thanks,
    Very useful. I made $cBits = 32 - $cbits for normal cidr.
    Now the question is, does this produce the minimal set?
    Regards
    Dino

      Thanks for catching that I was counting the bits backward.

      Yes, it produces the minimal set.

              - tye (but my friends call me "Tye")
Re: (tye)Re: converting complex netrange to cidr notation
by MeowChow (Vicar) on May 11, 2001 at 20:58 UTC
    Another interesting variant of this problem would be to find the minimal set of IP's + netmasks that cover a given range... hmm, I think a Golf outing is coming on :)

    update: Actually, I think these are equivalent problems, so never mind, probably.

       MeowChow                                   
                   s aamecha.s a..a\u$&owag.print

      For a single range, the above solution is the minimal one even if you allow arbitrary masks (though I haven't rigorously proved that -- just supporting your suspicion). If you allow multiple ranges, then the problem gets much harder and it becomes possible for arbitrary masks to provide smaller solutions.

              - tye (but my friends call me "Tye")

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