my %myUnitIfs;
processInterfaceData(\$config{units}{myUnit}{interfaces}, \%myUnitIfs);

##</code><code>##

processInterfaceData(\$config{units}{yourUnit}{interfaces}, \%yourUnitIfs);
processInterfaceData(\$config{units}{anotherUnit}{interfaces}, \%anotherUnitIfs);

##</code><code>##

sub processInterfaceData
{
  my ($h, $nh) = @_;
  print "$key\n"
   foreach my $key (keys %{$h});
}