can not ping with a simple switch config

Dear all,
I have a simple switch with EtherSwitch, as follows:

1 switch :: EtherSwitch;
2
3 queue1 :: Queue;
4 queue2 :: Queue;
5 queue3 :: Queue;
6 queue4 :: Queue;
7
8 FromDevice(eth6) -> [0]switch;
9 FromDevice(eth7) -> [1]switch;
10 FromDevice(eth8) -> [2]switch;
11 FromDevice(eth9) -> [3]switch;
12
13 switch[0] -> queue1 -> ToDevice(eth6);
14 switch[1] -> queue2 -> ToDevice(eth7);
15 switch[2] -> queue3 -> ToDevice(eth8);
16 switch[3] -> queue4 -> ToDevice(eth9);


I have four servers h1, h2, h3, h4 connect to eth6, eth7, eth8 and eth9
of click host respresently.
When I ping h2 from h1, the screen tells that the destination is
unreachale.

But when I start tcpdump on eth6 and eth7, then I can ping h2 successufully.

Is there any ideas about that?

Thanks anyway.