I'd try another solution :)
why not to read all IP adresses, convert them to binary,
for each part do:

join "", unpack "B8", pack "I" , $value;
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, getting rid of '.' (couse now they play no role)
write these adresses to a txt file and then sort them execing external 'sort'?
Then convert them back to decimal , '.'-separated.. and voi la...
I havent tested that, but it seems to me it'll be quicker.

/Maqs.