I've tried inet_ntoa and friends

Presumably you have lost the Network byte packing somewhere because there is no problem converting your quoted integers into realistic dot quads.....

my $addr = pack "N", -1062731776;
my $mask = pack "N", -256;

use Socket;
print inet_ntoa($addr),"/",inet_ntoa($mask),"\n";


sub perl_ntoa { join ".", unpack( "C4", $_[0] ) }
print perl_ntoa($addr),"/",perl_ntoa($mask),"\n";

__DATA__
192.168.0.0/255.255.255.0
192.168.0.0/255.255.255.0
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