use strict;
use warnings;

use Data::Dumper;

my %components = (
   COMP1 => {
	        eth1    => q{10.172.9.21/24},
	        eth1_gw => q{10.172.1.1},
	        eth2    => q{10.172.10.21/24},
	    },
   COMP2 => {
	        eth1    => q{10.172.9.22/24},
	        eth2    => q{10.172.11.21/24},
	    },
   COMP3 => {
	        eth1    => q{10.172.11.21/24},
	        eth2    => q{10.172.13.21/24},
	        eth3    => q{10.173.2.98/24},
	    },
  );

my %byIP = ();
foreach my $comp ( keys %components )
{
    foreach my $eth ( keys %{ $components{ $comp } } )
    {
        push @{ $byIP{ $components{ $comp }->{ $eth } } },
           qq{$comp:$eth};
    }
}

print Data::Dumper->Dumpxs( [ \ %byIP ], [ qw{ *byIP } ] );