ipsec and gre on the same interface

Hi,

I've got a set up with two boxes (routers) with ipsec and gre (quagga for the 
routing) that works but that includes 2 different interfaces in each box. But 
I would like to do this in a box with only one interface for ipsec and gre. Is 
that possible? In a vmware setup I have eth0 and eth1 as my two interfaces and 
established an endpoint for the gre tunnel in eth1 I can get ipsec and gre 
running and forwarding packets. But when I want to do the same thing with only 
one interface it doesn't work.

Am I doing something really stupid or should this work? If I'm doing something 
really stupid could you explain what?


The setup

Working setup

       ****          ****                                                 
       *  *----------*  *                                                 
       ****          ****                                                 
              ipsec                                                            
           <-------->                                                     

              gre 
       <----------------> 



The setup I would like to get working

       ****          ****                                                 
       *  *----------*  *                                                 
       ****          ****                                                 
              ipsec                                                            
           <-------->                                                     

              gre 
           <--------> 


regards,


/bengan