基于状态的切换

RouterA

Router-A#configure terminal
Enter configuration commands, one per line.End with CNTL/Z.
Router-A(config)#access-list 11 permit any
Router-A(config)#ip nat pool NATPOOL172.17.100.100 172.17.100.150 netmask 255.255.255.0
Router-A(config)#ip nat inside source list11 pool NATPOOL mapping-id 1
Router-A(config)#interface FastEthernet0/0
Router-A(config-if)#ip address 192.168.1.3255.255.255.0
Router-A(config-if)#ip nat inside
Router-A(config-if)#standby 1 ip192.168.1.1
Router-A(config-if)#standby 1 preempt
Router-A(config-if)#standby 1 nameSNATGROUP
Router-A(config-if)#exit
Router-A(config)#interface Serial0/0
Router-A(config-if)#ip address 172.17.55.2255.255.255.252
Router-A(config-if)#ip nat outside
Router-A(config-if)#exit
Router-A(config)#ip nat Stateful id 1
Router-A(config-ipnat-snat)#redundancySNATGROUP
Router(config-ipnat-snat-red)#mapping-id 1
Router(config-ipnat-snat-red)#exit
Router-A(config)#end
Router-A#

RouterB

Router-B#configure terminal
Enter configuration commands, one per line.End with CNTL/Z.
Router-B(config)#access-list 11 permit any
Router-B(config)#ip nat pool NATPOOL172.17.100.100 172.17.100.150 netmask 255.255.255.0
Router-B(config)#ip nat inside source list11 pool NATPOOL mapping-id 1
Router-B(config)#interface FastEthernet0/0
Router-B(config-if)#ip address 192.168.1.2255.255.255.0
Router-B(config-if)#ip nat inside
Router-B(config-if)#standby 1 ip192.168.1.1
Router-B(config-if)#standby 1 priority 90
Router-B(config-if)#standby 1 preempt
Router-B(config-if)#standby 1 nameSNATGROUP
Router-B(config-if)#exit
Router-B(config)#interface Serial0/0
Router-B(config-if)#ip address 172.17.55.6255.255.255.252
Router-B(config-if)#ip nat outside
Router-B(config-if)#exit
Router-B(config)#ip nat Stateful id 1
Router-B(config-ipnat-snat)#redundancySNATGROUP
Router(config-ipnat-snat-red)#mapping-id 1
Router(config-ipnat-snat-red)#exit
Router-B(config)#end
Router-B#

注释虽然说通过使用HSRP可以解决可用性的问题，但是不能同步NAT翻译表，从12.2(13)T以后思科引入了基于状态的NAT（SNAT），这样可以保持两台设备的翻译表同步，其关键命令为ip nat Stateful 要注意的是这里的Stateful是大写开头的，这里是区分大小写的。另外SNAT只和HSRP连用，不能跟VRRP或者GLBP一起作用。同时也可以使用多组HSRP的形式来保持负载均衡。