In this post I would like to demonstrate how NAT works on Cisco IOS router and more particularly what is the order of operation process when using Domain-based NAT vs. Nat Virtual Interface (NVI). As usual, to highlight the different configuration examples throughout this post I will use the following topology:
Let´s imagine that R1 is simulating a virtual PBX (also known as Hosted PBX.) located in the Voice provider network. This VPBX needs access to R5 (which is simulating a Lotus Notes server) in order to synchronize the different information for calendar, contacts, etc. Here are the following requirements from the customer:
- The customer doesn´t want to run any dynamic routing protocols between its network and the Voice provider network
- The customer wants the implementation of the solution to be as transparent as possible.
- The voice provider must only have access to the lotus notes (represented by R5 in this scenario).
- The voice provider must not be aware of any internal networks located at the customer site.
- The Voice provider has installed a tiny software client on each PC located at the customer site on the 192.168.100.0/24 network in order to send information to the VPBX. This software should be able to reach the VPBX (simulated by R1 in this scenario) without having any routing information regarding the Voice provider network.