Nodes on different hosts don't communicate

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In my environment, subscriber node on host-S can't get a message of publisher on host-P.

For example, in very simple tutorial like this, nodes don't exchange messages. As in the snapshot of rxgraph below, /rosout and /talker (publisher node) are visible. However they don't "shake hands".

Things suggested here are checked. netcat using the port numbers that are shown on rxgraph worked (of course after stopping nodes).

On web browser, opening http://%host-P's IP address%:11311/ returns following error:

Error response
Error code 501.
Message: Unsupported method ('GET').
Error code explanation: 501 = Server does not support this operation.

Environment:

Both: electric, inside of company's LAN 
Host-P: Ubuntu 11.04
Host-S: Ubuntu 10.10

Any comment would be appreciated. Thanks!