Hello Mulugeta,
You must open traffic to your SAP ERP Server ports 32NN, 33NN and 36NN, wher NN is the instance number of your system. If your instance number is 00, then you must open ports 3200, 3300 and 3600.
Check this document with SAP Ports:
http://www.garage4hackers.com/attachment.php?attachmentid=9&d=1284317492
Hope it helps.
Best regards,
Martina