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09 Apr 15 ip nat outside

IP NAT Outside

NAT – Network Address Translation, at times can be a complicated process depending on what you are trying to do and how it gets configured on a Cisco Router vs Cisco ASA’s is a bit different as well. This post is about recent NAT – Network Address Translation on a Cisco Router configuration that I had to do. Need was to translate an Outside IP address that belonged to a server in our Data Center (Outside Global) into another IP address at a branch location as an Outside Local. Example Network scenario:

Local Subnet at Branch = 172.16.1.0/24
Server IP at Data Center = 10.10.10.250
NAT IP for the server = 2.2.2.2

Basically the need was to translate 10.10.10.250 to 2.2.2.2 at the local branch. Usually it is the other way around where we NAT all the internal IP Addresses going out. However in this case we were trying to do the reverse. Following commands were used:

ip nat outside source static 10.10.10.250 2.2.2.2
!
Interface fa0/0
description ### WAN ###
ip nat outside
!
interface fa0/1
description ### LAN ###
ip nat inside

Now when the clients from 172.16.1.0/24 network attempted to connect to 2.2.2.2, branch router would translate that to 10.10.10.250 and route it to the Data Center server. Return packet would come from 10.10.10.250 and would get translated to 2.2.2.2 and then to the client(s) on the 172.16.1.0/24 network.

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