SAP NW Gateway behind firewall issue

Hello experts,

We are implementing SAP Fiori for a client. They have installed NW Gateway on SAP ECC (Embedded approach). SAP ECC (and GW) are behind firewall and they cannot be accessed externally.

I would like to know how do I use WebServer/Reverse Proxy to access NetWeaver Gateway and oData services through firewall.

Any guidance / document / cook book will be highly appreciated.

Thanks!

Tej