Marius,
172.31.255.254 is merely my tunl0 IP address, it's a Private IP in the Class B range, using a /32 (a single host on the network), nothing works using that IP address but ping from my 44LAN.
44.60.44.1 is the IP of my eth1 interface, everything is handled on my device via IP forwarding.
I have my tunnel isolated from my 44LAN and Local/WAN network for testing and troubleshooting purposes. This ensures that I'm in fact routing if a packet moves from one network to another. My eth0 is my public facing LAN - which has a 192.168 IP scheme, IP-in-IP is passed to that network from my Public IP address by my Router. eth1 is my 44LAN with the IP address of 44.60.44.1/24.
my setup script can be seen at http://44.60.44.13/startampr
73,
Lynwood KB3VWG