Tunnel on 2500 - possible szenario?

[ak8899]

We want to place a Cisco2500 between our Firewall and the router connecting to the internet. The Cisco 2500 should be the start of a GRE Tunnel going trough the internet to another Cisco device at a client's site. We want to use either the Ethernet 0 or loopback 0 interface as the tunnel source. So we use only one physical interface, ethernet 0, is this a valid configuration?
A second step would be the config of IPSec. Any comments/hints are greatly appreciated!
(We can use public addresses for all subnets)


router1#
Using 1048 out of 32762 bytes
!
version 11.3
service timestamps debug uptime
service timestamps log uptime
service password-encryption
!
hostname router1
!
enable secret xy
enable password xy
!
ip subnet-zero
no ip finger
ip domain-name xy.com
ip name-server x.x.x.x
ip multicast-routing
isdn switch-type basic-net3
!
!
process-max-time 200
!
interface Loopback0
ip address 1.1.1.1 255.255.255.0
!
interface Tunnel0
description Tunnel Test
ip address 1.1.2.1 255.255.255.0
tunnel source Loopback0
tunnel destination 2.2.2.1
!
interface Ethernet0
ip address 1.1.3.1 255.255.255.0
!
interface Serial0
no ip address
no ip mroute-cache
shutdown
no fair-queue
!
interface Serial1
no ip address
shutdown
!
interface BRI0
no ip address
shutdown
isdn switch-type basic-net3
!
router rip
network 1.1.0.0
!
no ip classless
ip route 0.0.0.0 0.0.0.0 <internet Router>
!
!
end
regards,
Alain