foreach $srcip (keys(%srciphash))

##</code><code>##

foreach $dstip (keys(%{$srciphash{$srcip}}))

##</code><code>##

$srciphash{$srcip}{$dstip} = 1;

##</code><code>##

my %srciphash = (
  foo => { one => undef },
  bar => { two => undef },
  baz => { three => undef },
);

foreach my $srcip(keys %srciphash) {
  foreach my $dstip(keys %{ $srciphash{ $srcip } }) {
    print "$srciphash{$srcip}{$dstip} = 1\n";
  }
}

__output__

$srciphash{foo}{one} = 1
$srciphash{baz}{three} = 1
$srciphash{bar}{two} = 1