# data file
(
    # Quoting the dotted quads since => will not quote 
    # those correctly
    '10.0.0.128' =>
        {
           '10.0.0.129'=>3,
           '10.0.0.129'=>4,
           '10.0.0.130'=>3,
           '10.0.0.131'=>2,
           '10.0.0.132'=>1,
           '10.0.0.133'=>1,
           '10.0.0.134'=>2,
           '10.0.0.135'=>4,
           '10.0.0.136'=>1,
           '10.0.0.137'=>4,
           '10.0.0.138'=>3
        },
    '10.0.0.129' =>
        {
           '10.0.0.128'=>3,
           '10.0.0.130'=>1,
           '10.0.0.131'=>2,
           '10.0.0.132'=>1,
           '10.0.0.133'=>2,
           '10.0.0.134'=>1,
           '10.0.0.135'=>2,
           '10.0.0.136'=>3, # the > was missing on this line...
           '10.0.0.137'=>3,
           '10.0.0.138'=>4
        },
);
[download]

my $x=join "",<FILE>;
my %graph = eval $x;
[download]

Now your reading code can simply be:

my $x=join "",<FILE>; 
my %graph = eval $x;
[download]

Please don't use string-eval to read data files. CPAN has several data file readers that don't crash your program or erase your harddisk if the data file contains unexpected data. Think about JSON, YAML, or, if you have no better idea, XML. None of those formats is read as executable code.

And if you really can't avoid string-eval, at least use Safe in a "deny-almost-everything" configuration.

Alexander

--
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)