Using each for navigating hashes can clean things up a little:

use strict;
use warnings;

my %netMap =
    (
    'LSS1' =>
        {
        'LUN1' => [qw(HOST1 HOST2 HOST3)],
        'LUN2' => [qw(HOST1 HOST2)],
        },
    'LSS2' =>
        {
        'LUN3' => [qw(HOST5 HOST6)],
        'LUN4' => [qw(HOST1)],
        },
    );

while (my @entry = each %netMap) {
    print $entry[0] . "\n";
    while (my @lun = each %{$entry[1]}) {
        print "    $lun[0]\n";
        print "        $_\n" for @{$lun[1]};
    }
}
[download]

Prints:

LSS2
    LUN4
        HOST1
    LUN3
        HOST5
        HOST6
LSS1
    LUN2
        HOST1
        HOST2
    LUN1
        HOST1
        HOST2
        HOST3
[download]

The down side is that you can't control the output order, it is dictated by the enumeration order returned by each.