Stateful NAT allows you to configure routers to synchronise their NAT tables. It is useful in situations where you have redundant gateways and need the traffic to flow uninterrupted in the event of a failover. The first thing to setup is the stateful NAT mapping id. This determines how the routers communicate their NAT information. You can configure the synchronisation to use either UDP or TCP. The redundancy name should be used in the HSRP configuration later. ip nat Stateful id 1 redundancy HSRP_IN mapping-id 1 as-queuing disable protocol udp We now need to create the NAT and HSRP settings on the interfaces. Obviously we are setting the NAT inside and outside. The HSRP is tracking the opposite interface so that the priority is reduced if it fails triggering a failover. interface FastEthernet0/0 ip address 10.44.0.2 255.255.255.0 ip nat inside ip virtual-reassembly duplex auto speed auto standby ip 10.44.0.1 standby priority 110 standby preempt standby