GRE tunnel and a ipv4 subnet /29

I have an ipv4 test subnet from extraip 37.x.y.0/29

My internet connection has ip-address a.b.c.d.
I've a Fritxbox router and behind NAT is my FreeBSD server with 
ip-address 10.10.10.15.
On this router I've opened the firewall for GRE to my FreeBSD server.
On my FreeBSD server rc.conf has the following lines:

cloned_interfaces=“gre0”
ifconfig_gre0=“inet 37.x.y.2 37.x.y.1 netmask 255.255.255.248 tunnel 
a.b.c.d gatewayip”
static_routes=“tunnel”
route_tunnel=“37.x.y.0/29 37.x.y.1”

This doesn't work. Whats wrong? Do I forget something?

Jack Raats