Static NAT overloaded???

Static NAT is a one-to-one mapping between a local address and a global address. But, what if you have 2 local addresses that map to the same global address?

Well, you would have an overloaded static NAT, which doesn't make much sense because the router wouldn't know which device to send return traffic to.

For example:

Router(config)# ip nat inside source static 192.168.1.10 200.1.1.10
Router(config)# ip nat inside source static 192.168.1.20 200.1.1.10

In this scenario, both internal hosts 192.168.1.10 and 192.168.1.20 are mapped to the same external address 200.1.1.10. When return traffic comes back from the internet destined for 200.1.1.10, the router has no way to determine whether it should forward the packet to 192.168.1.10 or 192.168.1.20.

The router will typically use the first matching entry in the NAT table, which means:

• All return traffic will go to 192.168.1.10
• Host 192.168.1.20 will never receive return traffic
• This creates connectivity issues for the second host

The solution? Use different global addresses for each static NAT mapping, or consider using PAT (Port Address Translation) if you need to conserve public IP addresses.

Static NAT should maintain the one-to-one relationship principle to function correctly.