How to configure GNS3 to a virtual box client.

To configure the GNS3 with a virtual box client follow these steps-
1.-->  Start the gns3 and drag a router from the list and drop it to the working windows.
2.-->  Like router also drag a cloud and drop in working window.

3.--> Now Double click on cloud and select a C1 menu on the left hand list .
         after that select NIO ethernet tab.Here is the drop down list in which select a  virtual
        Box host only network. add this and apply the settings.

4.--> Attach a fast ethernet cable between router and cloud virtual box interface.

5.--> Configure the router with a ip address its interface ip address- 192.168.1.254/24.
6.--> Start the Virtual machine and select the settings tab right click on the os level.
        select network tab-->adapter 1->attached to-->Host only network.

7.--> Give the Ip address to virtual box connection of the main platform -192.168.1.1/24.
    and also configure the  virtual client with  same network ip address - 192.168.1.2/24.

8.--> Now ping the router virtual box client ip address.

Now the GNS3 it configured with virtual box client.

For Further Reading,

General, How To, Networking, Software and Apps