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Re: 16 year old bug

    Date:        Tue, 24 Aug 2010 08:43:52 -0400
    From:        Michael Richardson <>
    Message-ID:  <>

  | There is only one reason to use non-contiguous IP masks for *ROUTING*
  | tables (vs for IPsec SPDs, where a there might be multiple IP subnets in
  | the 5-tuple):
  |     IPv4 scarcity

It actually doesn't help for that at all.   Ambiguous masks might,
perhaps, but they just don't work, and never did.   But non-contig
masks (the simple ones) can always be turned into contig ones by just
moving the bits in the addresses around (and hence renumbering hosts).
Since there is a contig mask for every non-contig (simple) scheme that
you can devise, using non-contig itself cannot possibly have any effect
upon address usage.   It just saves renumbering effort (occasionally).

And some people consider it sexy...


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