GRE over IPSec tunnels between Cisco and Linux

Stuff: GRE over IPSec tunnels between Cisco and Linux (openswan)
http://ghergamilan.blogspot.tw/2010/06/gre-over-ipsec-tunnels-between-cisco.html

        leftprotoport=47                       #match the GRE traffic, this line is very important
        rightprotoport=47                     #match the GRE traffic