If you're going to be using a referenced hash then the following code will do the trick for you. It gets a little confusing when to use {} and when to use (), at least I would always get these mixed up.

#! /usr/local/bin/perl

use warnings;
use strict;

my $allData = {
        src1 => {
                dest1 => '112.112.112.112',
                dest2 => '112.112.112.113'
                },
        src2 => {
                dest1 => '192.168.1.101',
                dest2 => '192.167.1.102'
                }

};

foreach my $source ( keys %{$allData}){
        foreach my $dest (keys %{$allData->{$source}}){
                #blah
        }
}
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Hope that makes sense or helps.
Cheers!