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

##</code><code>##

foreach my $compName (keys %components) {
  foreach my $param (keys %{$components{$compName}}) {
    if ($param =~ /eth[0-9]$/) {
#  [ then loop again through the COMP keys, excluding the current key 
#    ... does not seem nice ]
    }
}