Troubleshooting NAT on Cisco Routers
Troubleshoot NAT issues by verifying inside/outside interfaces, checking ACLs, and utilizing commands like `show ip nat translations` and `debug ip nat`.
Common NAT Misconfigurations
The most frequent NAT issues stem from forgetting to apply `ip nat inside` and `ip nat outside` to the correct interfaces, or configuring the Access Control List (ACL) incorrectly.
Useful Show Commands
- `show ip nat translations`: Displays active translations. - `show ip nat statistics`: Shows hit rates, misses, and the number of active translations.
Using Debug IP NAT
For live troubleshooting, `debug ip nat` shows translations as they occur. Ensure you limit traffic during debugging to avoid overwhelming the router CPU.
❓ Frequently Asked Questions
Why is my NAT translation table empty?
Ensure traffic is actually flowing, your ACL is matching the traffic, and interfaces are defined as inside/outside.
How do I clear the NAT table?
Use `clear ip nat translation *`. Note that static translations will not be cleared.
What happens if the ACL denies traffic?
If the ACL denies the traffic, the NAT process will ignore it, and it will not be translated.