You enter the show ip nat translations command and do not see any translations. You are worried that there is a problem. What would be the most appropriate action to test the NAT operation?
- Issue a ping from the router to any IP address in the outside network.
- Verify the running configuration to find the configuration error.
- Issue a ping from a device inside the network that should be translated.
- Issue a traceroute from the router to any IP address in the outside network.
Explanation: In Cisco NAT operations, specifically for dynamic NAT and Port Address Translation (PAT), translation entries are not permanent and are only created when relevant traffic passes through the router. According to the sources, a router determines that a source address must be translated only when it receives the first packet from an internal host on a NAT-enabled inside interface.
If the show ip nat translations command shows an empty table, it is often because no active sessions are currently being translated or previous dynamic entries have timed out due to inactivity. Therefore, to test the NAT operation and populate the table, you should generate traffic (such as a ping) from an internal device that is eligible for translation.
Other actions are less effective for testing:
- Pinging or tracing from the router itself will typically use the router's own IP address, which is often already a public/global address and does not require translation, thus failing to test the logic intended for internal private hosts.
- Verifying the configuration is a troubleshooting step to take after a test has failed, rather than the primary method to test the operation of the NAT engine itself.
Related exam: Modules 8 – 13: Checkpoint Exam: Network Routing Answers (CCNP ENCOR v9)
