GRE tunnel through firewall

Hello all,

I am trying to setup a GRE tunnel between 2 routers, one of which is located behind an Astaro firewall. I have setup NAT and packet filter rules on the firewall to pass all GRE traffic into the router on the inside of the firewall. As a test I also setup the rules to allow ALL traffic to pass to the inside router. Anyone successfully done something like this?

Thanks

Dave