.测试拓扑：
参考链接：http://www.cisco.com/en/US/products/sw/secursw/ps2308/products_configuration_example09186a008073b06b.shtml
总的思路：在EzVPN Server上设置一个loopback口，并在外网口配置route-map，将客户端去往公网的流量打到loopback口并进行NAT出公网，配置route-map时需要注意下一跳地址为loopback口任意直连地址，而不是loopback口的地址。
2.基本配置：
A.Private路由：
interface E0/0
ip address 172.16.1.10 255.255.255.0
no shut
ip route 0.0.0.0 0.0.0.0 172.16.1.1
B.Branch路由器：
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
no shut
interface Ethernet0/1
ip address 202.100.1.1 255.255.255.0
no shut
ip route 0.0.0.0 0.0.0.0 202.100.1.10
C.Internet路由器：
interface E0/0
ip address 202.100.1.10 255.255.255.0
no shut
interface E0/1
ip address 202.100.2.10 255.255.255.0
no shut
D.Center路由器：
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0
ip nat inside
no shut
interface FastEthernet0/1
ip address 202.100.2.1 255.255.255.0
ip nat outside
no shut
ip route 0.0.0.0 0.0.0.0 202.100.2.10
ip access-list extended pat
deny ip 10.1.1.0 0.0.0.255 123.1.1.0 0.0.0.255
permit ip any any
ip nat inside source list pat interface FastEthernet0/1 overload