Is it possible to reach a system in public network through a system in private network using gre tunnel ?

Question

I have a system in private network and a server with public ip which i was accessing through ppp links to a router which could reach the system over internet.
But now i want to use gre tunnels between the router and the server to access the same server .
How can achieve the same ?

Comments

I hope I understood your problem correctly,
Both Server and Router should understand GRE protocol in this particular case and should have the capability to decapsulate the IP Packet within the GRE Tunnel.

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Thanks for your response Salil.
Assume Server and Router understand GRE protocol.
I am mostly worried about the routes to be added on router for the logical GRE interface and physical ethernet interface for reaching the server.

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Yes route (route_add) has to be there so that there is a link between the router and server.
I am telling this from basic networking point of view rather then GRE point. In short u must able to ping from router to server or vice versa to achieve anything further.