use strict;
use warnings;
while(<DATA>){
   chomp;
   my $mask = (split(/\s+/, $_))[2];
   print "Mask $mask is ", &Valid($mask), "\n";
}

sub Valid {
   my @octs;
   local $_  = shift;

   return 0  if !defined $_;
   return 0  if m{(?:(?:^|\.)[^0]\d*\.)(?!255)};
   return 0  if (@octs = split(/\./, $_)) ne 4;
   return 0  if grep {!m/^(?:0|3|7|15|31|63|127|255)$/} @octs;
   return 1;
}
__DATA__
field1 10.1.253.11  0.0.0.0
field1 10.1.254.0  0.0.0.64
field1 10.1.254.128  0.0.0.63
field1 10.1.158.0  15.255.0.255
field1 10.1.160.0  0.0.0.37
field1 10.1.161.0  0.0.146.255
field1 10.1.161.0  0.0.255
field1 10.1.161.0  0.0.255.255
field1 10.1.161.0  255.0.0.0
field1 10.1.158.0  15.255.255.127