A hash key ($nas) is nothing more than a key and it has a corresponding value in the hash. That value may be a reference to another data structure (an anonymous hash). That anonymous hash may have one or more keys ($response_status). Your confusion is in thinking that there is only one possible value in the anonymous hash. In reality, it may have one or more keys. I would suggest the following code instead:

#!/usr/bin/perl
use strict;
use warnings;

use constant STATUS  => 0;
use constant REQUEST => 1;

# Some code that initializes %list
# In the form
# $list{ $nas }[STATUS]  = $response_status;
# $list{ $nas }[REQUEST] = $request_date_time

# Later on you can retrieve the status and request like

my $mac = ''; # actual code to get MAC from log
my $status  = $list{ $mac }[STATUS];
my $request = $list{ $mac }[REQUEST];
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Maybe I'm totally misunderstanding you, but I'm envisioning that you have a HoH structure like this:

my %macs = (
  '00:11:22:33:44:55' => {
    'response_status' => 12,
    'response_date'   => 'yesterday',
  },
  'AA:BB:66:12:13:14' => {
    'response_status' => 0,
    'response_date'   => '2004-12-31',
  },
  # ... and so on
);
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And you get some user input, then you look up the data you want:

my $mac = <STDIN>;
chomp $mac;

if ( exists $macs{$mac} )
{
  print "Okay, found mac $mac:\n";
  print "response_status: $macs{$mac}{response_status}\n";
  print "response_date:   $macs{$mac}{response_date}\n";
}
else
{
  print "Sorry, don't recognize that mac\n";
}
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Is that what you meant?

push @{ $list{$macaddress} }, [ $response_status, $request_date_time ]
+;
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