in page "http://wiki.ros.org/ROS/NetworkSetup"

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This is just an example how you can debug the network setup.

Directly below the line with the ssh hal and ping marvin, it says you should check the section Name Resolution on this page.

Do you have two computers with the following network configuration (hostname/IP)?

marvin.example.com : 192.168.1.1

hal.example.com : 192.168.1.2

If not, this is clear. You need to properly configure your computers to follow this example as it is on the page....