Let's take today about the stateful Nat [ SNAT] -This is Feature give us translation more than one network address which mean Back up nat to the active failure.  - Nat is great feature help us to permit the interconnection of private network to reach the Public network. - SNAT work as active and back up scenario the active handle the traffic require translation ip address from Private to public. - Back up SNAT is working as duplication all the translation which in the active table and once the active translator is down the back up will handle the translation and will replay to all requests.  - There is Two phases of the SNAT , phase one was  not supported for the application level,  Phase two is provide the application level and asymmetric routing [ Encryption method use two Keys to encrypt the plain text secret key is change over the internet] recommend to read one fully article about the asymmetric & symmetric. -The mapping-id must be the same between them -Redundancy string must match the standby name.   Example for the SNAT configuration :  -------------------------------- Interface Gig 0/0/0 Description SNAT Standby 10 name SNAT-DC standby 10 ip address 10.100.101.254 ip nat inside  -----  interface Gig 0/0/1 Ip nat outside  ---- IP nat stateful id 10 redundancy SNAT-DC Mapping-id 90 ---------------------------- access-list nat  10 permit 10.100.101.0 0.0.0.255  Ip nat pool SNAT-POOL 37.0.0.100 37.0.0.100 prefix-length 24  Ip nat inside source list nat pool  SNAT-POOL mapping-id 90 overload  --------- router bgp 6508 bgp router-id 10.10.10.10 no  bgp default    ipv4-unicast neighbor 38.0.0.100 remote-as 6509 address-family ipv4 network 37.0.0.100 mask 255.255.255.0 exit ------------ some of commands help for T-shoot  Show ip snat peer  show ip snat distributeed   show ip snat distributed verbose   show standby   ... View more