Probably not short enough to be worth it, but this works for me on unix (perl v5.12.2), and I think it has a chance to work on windows, too: 
perl -anF"/\./" -E "chomp@F;say join q{.},reverse@F" zones.txt
10.100.1
10.100.2
10.100.3

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In reply to Re: One liner help by toolic
in thread One liner help by VinsWorldcom

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