线路备份都是在几秒内完成的，但相对的NAT time-out的时间至少有5分钟，在这5分钟内，整个网络都是无法访问的，可以通过设置NAT time-out来实现，但太小的time-out轻易导致更重的网络负载。这个问题可以通过route-map配合nat来实现。
这个试验采用一个串口代替isdn拨号端口。双静态路由代替dynamic routing来实现。其中需要转换的源地址可以定义ACLs进行取代。
!
version 12.0
service timestamps debug uptime
service timestamps log uptime
no service passWord-encryption
!
hostname r2514
!
enable secret 5 $1$EkUC$WUTRmsOG.bMfJ7AwcUpur0
enable password cisco
!
ip subnet-zero
no ip domain-lookup
!
!
!
interface Ethernet0
ip address 192.168.1.222 255.255.255.0
no ip directed-broadcast
ip nat inside
no ip mroute-cache
!
interface Ethernet1
no ip address
no ip directed-broadcast
no ip mroute-cache
shutdown
!
interface Serial0
ip address 172.16.10.2 255.255.255.252
no ip directed-broadcast
ip nat outside
encapsulation ppp
no ip mroute-cache
clockrate 125000
!
interface Serial1
ip address 172.16.20.2 255.255.255.252
no ip directed-broadcast
ip nat outside
no ip mroute-cache
!
ip nat inside source route-map bak-nat interface Serial1 overload
ip nat inside source route-map bck-nat interface Serial0 overload
ip classless
ip route 0.0.0.0 0.0.0.0 172.16.10.1
ip route 0.0.0.0 0.0.0.0 172.16.20.1 2
!
logging trap debugging
logging 192.168.1.119
Access-list 12 permit 192.168.1.222
route-map bck-nat permit 10
match interface Serial0
!
route-map bak-nat permit 20
match interface Serial1
!
snmp-server community public RO
!
line con 0
transport input none
line aux 0
line vty 0 4
password cisco
login
!
end
