Cisco – How to built a static nat from an outside address to an inside address on Cisco

cisconat;

I'm not used to doing NAT on Cisco devices, and I'm tasked with bringing in traffic being sent to a public address that is routed to our gateway. I would like to NAT the traffic from our gateway (a Cisco 2901 router running IOS 15.0) to a private address.

From what I've read, I think this might work but I have a feeling I'm missing something.

interface GigabitEthernet0/1.1
ip address 63.145.168.58 255.255.255.252
ip nat outside

interface GigabitEthernet0/0.1
ip address 10.2.0.3 255.255.0.0
ip nat inside

ip nat inside source static udp 10.0.1.40 5060 72.165.117.130 5060 extendable

72.165.117.130 is one of our private (MPLS) WAN addresses that routes to 63.145.168.58. I'm trying to forward traffic sent to that address to an internal device at 10.0.1.40.

Is that all there is to creating a one-to-one NAT, or am I missing something?

Best Answer

I think you didn't quite understand the concept of NAT.

NAT means hiding your private IP address(es) behind the public address(es) of your router's external interface; with NAT, you can:

  • Have a packet start from one of your internal addresses (10.0.1.40) go outside your network and look to external devices like it originated from your router's external address (63.145.168.58), and
  • Have a packet come from outside your network to some port on your router's external IP address (63.145.168.58) and be forwarded by your router to one of your internal addresses (10.0.1.40).

But if a packet is going to some completely different address which is not managed by your router (like 72.165.117.130) and is not passing through the router itself, there's nothing at all the router can do to "intercept" it and forward it to some other destination.

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