NAT-Loopback (Hairpin NAT)
NAT-Loopback, also known as Hairpin NAT, allows devices within a local network (LAN) to access an internal server via its public IP address.
Normally, a request to one's own public IP fails when originating from the internal network. With NAT-Loopback, the router recognizes that the destination of the request (the public IP) is assigned to an internal host and loops the data packet back into the local network.
- Scenario: An internal client accesses
example-server.ch. - Without NAT-Loopback: The connection is dropped because the router typically discards packets from internal to its own external IP.
- With NAT-Loopback: The router recognizes the destination IP as its own and routes the request directly to the internal IP of the target server.
Activation and usage​
- No manual configuration required: NAT-Loopback is enabled by default on the Centro Business.
- How it works: The function is immediately available once a port forwarding rule has been configured.
Limitations​
- None
FAQ NAT-Loopback​
What benefit does NAT-Loopback provide?
It enables consistent reachability of services. Users and applications can use the same address (e.g. for a cloud instance or mail server) regardless of whether they are on the local network or the external internet.
What can I check if NAT-Loopback is not working?
If access via the public IP/DNS from internal fails, check the following points:
- Port Forwarding: Is the rule correctly set up and active for the correct internal IP address of the target device?
- Service status: Is the relevant service (e.g. web server, database) running on the target client and is it switched on?
- Local test: Does access work within the LAN when using the server's internal LAN IP directly? If not, the problem lies with the server or its local firewall.
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