interface GigabitEthernet0/1
 description WAN
 ip address 1.1.1.1 255.255.255.224

crypto isakmp policy 10
 encr aes 256
 authentication pre-share
 group 2
 crypto isakmp key Secret-Key address 2.2.2.2
 !
 crypto ipsec security-association replay window-size 1024
 !
 crypto ipsec transform-set ESP-AES-SHA esp-3des esp-md5-hmac
 mode transport
 crypto ipsec nat-transparency spi-matching
 !
 crypto ipsec profile GRE
 set security-association lifetime seconds 86400
 set transform-set ESP-AES-SHA
 !
 interface Tunnel1
 ip address 10.10.20.1 255.255.255.252
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 ip mtu 1400
 ip tcp adjust-mss 1360
 load-interval 30
 keepalive 60 3
 tunnel source 1.1.1.1
 tunnel destination 2.2.2.2
 tunnel protection ipsec profile GRE