Hi,
I have different questions about tunnels management.
1) Imagine that you have 2 router (A,B) with a GRE Tunnel, but inside you have also 2 different routers o firewall with a vpn connection (image1 attached). Which would be the normal behavior? First GRE tunnel begin the communication about physical interface and inside this GRE tunnel exist a vpn connection?
2) I think I could be a ping from physical interface (out GRE and vpn), ping about GRE and ping about vpn, It's correct?
3) Which ports / protocols use GRE or VPN connections? Would be possible to permit / deny using acl's or a different resource? Would be possible to control these connections?