I'm trying to sort the keys of the following hash:

$VAR1 = {
  'GetNext -------------- 11.254.49.217:1.3.6.1.2.1.4.20.1.2' => {
    '1.3.6.1.2.1.4.20.1.3' => [
      [
        'ipAdEntNetMask',
        1
      ]
    ],
    'Min_Time' => '16:29:08.03',
    'Error_Status' => 'No error',
    'Avg_Time' => undef,
    'Min_Time_Diff' => '9:59:59.9',
    'Total_Time' => '0:00:00.0',
    'Last_Time' => '16:29:08.03',
    'Max_Time' => '16:29:08.03',
    '1.3.6.1.2.1.4.20.1.2' => [
      [
        'ipAdEntIfIndex',
        1
      ]
    ],
    'Max_Time_Diff' => '00:00.0'
  },
  'Response -------------- 11.254.49.217:1.3.6.1.2.1.4.20.1.3.0.0.0.0'
+ => {
    'Error_Status' => 'No error',
    'Total_Time' => '0:00:00.0',
    'Last_Time' => '16:29:08.04',
    '1.3.6.1.2.1.4.20.1.4.0.0.0.0' => [
      [
        'ipAdEntBcastAddr.0.0.0.0',
        1
      ]
    ],
    'Max_Time_Diff' => '00:00.0',
    'Min_Time' => '16:29:08.04',
    'Avg_Time' => undef,
    'Min_Time_Diff' => '9:59:59.9',
    '1.3.6.1.2.1.4.20.1.3.0.0.0.0' => [
      [
        'ipAdEntNetMask.0.0.0.0',
        1
      ]
    ],
    'Max_Time' => '16:29:08.04'
  },
  'GetNext -------------- 11.254.49.217:1.3.6.1.2.1.4.20.1.2.127.0.0.2
+' => {
    'Error_Status' => 'No error',
    'Total_Time' => '0:00:00.0',
    'Last_Time' => '16:29:08.04',
    '1.3.6.1.2.1.4.20.1.3.127.0.0.2' => [
      [
        'ipAdEntNetMask.127.0.0.2',
        1
      ]
    ],
    'Max_Time_Diff' => '00:00.0',
    'Min_Time' => '16:29:08.04',
    '1.3.6.1.2.1.4.20.1.2.127.0.0.2' => [
      [
        'ipAdEntIfIndex.127.0.0.2',
        1
      ]
    ],
    'Avg_Time' => undef,
    'Min_Time_Diff' => '9:59:59.9',
    'Max_Time' => '16:29:08.04'
  },
  'Response -------------- 11.254.49.217:1.3.6.1.2.1.2.2.1.12.20' => {
[download]

with this code...

my @key_hash = sort {
    $key_hash{substr($a,3)} cmp $key_hash{substr($b,3)}
} keys %key_hash;
[download]

I only need to look at the first three letters.
Any idea what I'm doing wrong?

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