需求：分支机构（R1）只有ADSL线路，需要与总部（R3）实现LAN能互访。

===========R3-HQ===============

crypto keyring PSK
pre-shared-key address 0.0.0.0 0.0.0.0 key cisco

crypto ipsec transform-set TS esp-3des esp-sha-hmac
!
crypto ipsec profile VTI
set transform-set TS

crypto isakmp profile DVTI
keyring PSK
match identity address 0.0.0.0
virtual-template 1

interface Virtual-Template1 type tunnel
ip unnumbered Loopback0
tunnel mode ipsec ipv4
tunnel protection ipsec profile VTI

interface Loopback0
ip address 192.168.1.3 255.255.255.0
!
!
interface Loopback100
ip address 10.23.0.3 255.255.255.0

!
interface GigabitEthernet0/0
ip address 100.23.0.3 255.255.255.0
!
!
router ospf 1
network 10.23.0.0 0.0.0.255 area 0
network 192.168.1.0 0.0.0.255 area 0

ip route 0.0.0.0 0.0.0.0 100.23.0.2

==========R1-Branch============

crypto keyring PSK
pre-shared-key address 0.0.0.0 0.0.0.0 key cisco
!
!
crypto ipsec transform-set TS esp-3des esp-sha-hmac
!
crypto ipsec profile VTI
set transform-set TS
!
interface Loopback0
ip address 192.168.1.1 255.255.255.0
!
!
interface Loopback100
ip address 10.12.0.1 255.255.255.0
!
!
interface Tunnel1
ip unnumbered Loopback0
tunnel source GigabitEthernet0/0
tunnel mode ipsec ipv4
tunnel destination 100.23.0.3
tunnel protection ipsec profile VTI
!

interface GigabitEthernet0/0
ip address 100.12.0.1 255.255.255.0

!
router ospf 1
network 10.12.0.0 0.0.0.255 area 0
network 192.168.1.0 0.0.0.255 area 0

!
ip route 0.0.0.0 0.0.0.0 100.12.0.2