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User unable to configure static NAT, receives the % Non-Static entry already exists error message


Core Issue

A static Network Address Translation (NAT) configuration is used for translating a particular local address to a specific global address and the other way around. Dynamic NAT creates translation entries in the NAT table when traffic received from a host matches the criteria specified for translation. Dynamic NAT also translates the address to a different address available in a configured pool. 

While attempting to configure static NAT (when dynamic NAT is already configured on the same router), the router may give this error message. This occurs if the address where the translation is being configured is already used by dynamic NAT and the translation entry exists in the table.


To resolve this problem and configure static NAT, perform these steps:

  1. Clear the existing entry from the NAT table by issuing the clear ip nat translation command from privileged EXEC mode.
  2. Modify the configured NAT pool to be used by dynamic NAT. This is done by issuing the ip nat pool command from global configuration mode. This ensures that the same address is not used by static as well as dynamic NAT.

    The router now allows static NAT to be configured successfully.

For more information, refer to Configuring Static and Dynamic NAT Simultaneously.

Other Errors, Warnings, and Log Messages

NAT - "%Non-Static entry already exists"


For some reason, a router we manage has converted a static entry to a dynamic entry all on it's own. Rancid shows a clear moment when the static entry disappeared from the running config; during a day when nobody logged in (logs confirm this).

Now when I try to add this static again, I get the "Non-Static entry already exists" message. There is no ip nat pool configured on this router, we do not use dynamic nat on this router. And yet show ip nat tran verbose seems to indicate the existing nat translations are dynamic - yes, the nat still works after the static was removed from the running config. Pretty weird.

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