Traditional Outbound NAT is designed to handle outbound connections, in which clients of the inside local network initiate requests to outside global Internet hosts. Bidirectional NAT, 2-Way NAT, or Inbound NAT is an enhancement upon NAT to handle connections initiated from the outside network.
The network setup on the figure above can be achieved using a single router. PC1 accesses PC2 using 172.16.1.3 outside local; while PC2 accesses PC1 using 192.168.1.3 inside global.
Bidirectional NAT configuration on RT1:
! interface FastEthernet0/0 ip address 172.16.1.1 255.255.255.0 ip nat inside ! interface FastEthernet1/0 ip address 192.168.1.1 255.255.255.0 ip nat outside ! ip nat inside source static 172.16.1.2 192.168.1.3 ip nat outside source static 192.168.1.2 172.16.1.3 add-route !
The add-route keyword adds a static /32 host route for the outside local address. This route is used for routing and translating packets that travel from the inside to the outside of the network.
RT1#sh ip route Gateway of last resort is not set 172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks C 172.16.1.0/24 is directly connected, FastEthernet0/0 S 172.16.1.3/32 [1/0] via 192.168.1.2 C 192.168.1.0/24 is directly connected, FastEthernet1/0 RT1#