Hi Vaibhav,
At the moment, the onPremise IS has to open up its firewall to allow the particular IP using which API Gateway Cloud will be connecting to the OnPremise endpoint. But there is a feature in the API Gateway Cloud roadmap to achieve this onPremise connectivity by a different mechanism which will not require this whitelisting of IP in the OnPremise.
Regards,
Karthik G
#API-Management#webMethods