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How to configure NAT with the "ip nat outside source" command

Core Issue

To translate the source address of the outside hosts in the traffic flowing from the outside to the inside network, issue the ip nat outside source command. In turn, this translates the destination address of the traffic from the inside to the outside network. 

Issuing this command is necessary in certain cases. For example, devices on private networks are usually addressed using private IP addresses, as defined by RFC 1918. Connectivity to the outside world is maintained  by using Network Address Translation (NAT) and translating to globally unique addresses assigned to the organization. Devices on private networks can also be addressed using IP addresses outside the RFC 1918 range. Connectivity is maintained by using NAT and translating to globally unique addresses. However, the device on the outside, whose global address is assigned to the inside hosts, is not able to communicate with the hosts on the private network due to overlapping addresses.

Resolution

Devices on the outside network can communicate with hosts on the inside network (despite overlapping addresses) by translating the source address of the traffic from the outside to the inside network. To enable NAT on the outside source address, issue the ip nat outside source command in global configuration mode.

For more information on configuring NAT by issuing the ip nat outside source command, refer to Sample Configuration Using the ip nat outside source static Command.

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‎06-22-2009 06:05 PM
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