Henry's Points

In the NAT world, there are two terminologies that we used often, one is Inside Local, and the other is Inside Global. Inside Local is those IP address hidden behind NAT. Inside Global is virtual IP address pool that can be accessed from outside world. Before configuring NAT, we need to define an access-list for INSIDE_LOCAL to define which IP address participate NAT process. We also need to define an IP pool for INSIDE_GLOBAL. Then, we can enable NAT

ip nat inside source list INSIDE_LOCAL pool INSIDE_GLOBAL overload

However, we still can’t ping outside from inside. Why? because INSIDE_GLOBAL are virtual IP addresses that outside routers don’t have route to it. To solve this problem, we have two options.

1. Create a loopback interface, assign IP address to the interface and let it running IGP in outside network.
2. Create a static route on NAT router and point it to Null0 interface. Redistribute the static route to IGP in outside network.

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