Description:
When using SAP Router then you can give a  VALID ROUTER STRING in "Application Server" field in Designer.

1) A Valid router String to connect to SAP System XYZ from router ABC would be
    /H/ABC/S/&ltPort Number>/H/XYZ/S/&ltPort Number>

where ABC is IP Address / hostname of your router. XYZ is IP Address / hostname of your SAP Application server

2)  If your router needs password then the string would be
     /H/ABC/S/&ltPort Number>/P/&ltYour Password>/H/XYZ/S/&ltPort Number>