Your split is using a regex like construct instead of split PATTERN, EXPR and the result (I think) is that you're splitting on $_, which isn't being set in the sub and who knows what it holds. Try:

my @a = split /./, $a->[0];  #split IP address on periods
...
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You didn't give any sample data so I can't say for certain if this is the problem, but it might be it.
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