IP NAT inside source vs IP NAT outside source


(Rene Molenaar) #1

This topic is to discuss the following lesson:


(Mohammad Hasanuz Zaman) #2

Hi Rene,

Thanks for your great lesson .I have a question regarding …

What is the used case of IP NAT OUTSIDE SOURCE Normally We don’t use the command. Need to know production network scenario .Many Thanks

BR//ZAMAN


(Lazaros Agapides) #3

Hello Mohammad

This is an excellent question. Take a look at this post:


This post may refer to a similar configuration using an ASA, but the concept is the same. This gives you a practical example where you would want to translate the outside address.

I hope this has been helpful!

Laz


(devaprem R) #4

Hi Rene

For NAT is it reuired for Router to have route for the NAtted IP

If i doing inside NAT 10.10.10.10 -> 20.20.20.20 on my R1 do my R1 required to have route for 20.20.20.20 ?

how will it handle the response traffic for 10.10.10.10 -> 20.20.20.2 , will it check rout table first or NAT first ?


(Lazaros Agapides) #5

Hello Devaprem

If you have a NAT translation between two addresses configured on a router, you don’t require any of those addresses to have a routing table entry in that specific router. These addresses are considered directly connected because they are associated with specific interfaces. For this reason, you don’t have to explicitly configure them for routing. However, other routers on the outside must have some routing information to be able to reach the 20.20.20.20 IP address but this is independent of NAT.

In general, when a packet arrives on an interface from outside to inside, it will translate NAT first and then route. More information about the order of operations in routers can be found at the following Cisco documentation.


I hope this has been helpful!

Laz


(devaprem R) #6

Thank you Laz , it clearly explains