Error : Failed to establish connection with report server.

Error : Failed to establish connection with report server. Verify the server URL is correct or review ULS logs for more information. Product area: SQL Server Reporting Services, Category: Configuration Pages

Answer : Use IP rather than Server name. Eg : http://IPADDRESS:80/ReportServer

Note : Before doing the Sharepoint SSRS config in Central Admin, we need to install the SharePoint 2010 Full installation (existing farm option).