NAT - Inside local, inside global, outside local, outside global

NAT example topology

In this post, I briefly summary NAT terms which are inside local, inside global, ouside local, and outside global.

I would like to elaborate the terms using the ablove topology.

 

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ip nat inside source static 10.10.10.1 171.16.68.5

 

interface s 0

ip nat inside

 

interface s 1

ip nat outside

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In order to verify the NAT tranlations, we can use show ip nat translations command.

 

If you look at the output above, you can grasp the difference between local and global.

Based on the router that handles NAT, it is local before ip translation occurs and global after that.

 

When the packet moves from the inside network to the outside network, the output is as shown below.

 

The protocol is displayed as icmp because NAT configuration is verified by ping.

In the same way, when receiving a packet from the outside, the settings for IP address translation can be done as follows.

 

ip nat outside source static 171.16.68.1 10.10.10.5

 

To sum up, the terms local and global are straight forward to understand. Also, the inside and outside keyward mean where they locate in the network.

 

Reference site: https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/4606-8.html