I've faced to an interesting thing at my GRE tunnels.sometime packets which I've defined a static route to tunnel as below don't route to GRE tunnel.
ip route x.x.x.x 255.255.255.255 Tunnel0
but when I remove it and add it after a short time it routes packets to tunnel again but maybe I face to this issue after less than a month and I've to do remove and add route again!!
Any advice would be appreciated.