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Help: NAT Loopback is working only half the time.

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camilaacolide

Occasional Visitor
Hello,

I have a RT-86U with version 384.17 which has been working perfectly since forever. I run a Raspberry Pi in my LAN with Nextcloud, and I could access it from anywhere using my DDNS (inside and outside the LAN). But last week, I had to reinstall it from scratch due to a corrupted SDCard. Since then, I am able to access it using my DDNS from outside my LAN reliably, but when accessing it from inside my LAN, it works only half the time. The other half of the time it errors with "connection refused", both on port 80 and 443.

It shouldn't be a problem with NAT loopback in the RT-86U, but I am without ideas of what could be happening. The router is connected directly to the internet, and the DDNS IP and the route WAN IP are the same. Could somebody help me?

Thanks.
 
Check your DNS server configuration (WAN and LAN).

You should really update to the current firmware release. Since you've had to set it up from scratch there's no reason not to.
 
Check your DNS server configuration (WAN and LAN).

You should really update to the current firmware release. Since you've had to set it up from scratch there's no reason not to.
I second this, if you are using a DNS record it may be resolving back to your public IP but from within your LAN you want the resolved address to be the local IP.
 
Well, right now I have created a dnsmasq.conf.add file mapping the domain name to the internal IP, and it fixed the problem (effectively working around the NAT loopback). But it was definitely not necessary before. Where can I check my DNS settings for misconfigurations?

Screen Shot 2022-05-09 at 17.17.13.png


Screen Shot 2022-05-09 at 17.17.30.png
 
Last edited:
That all looks fine. Assuming you're not using DNSFilter on the router I would look at the client setup.

As it happens "half the time" I would go to the command prompt on the effected machine and run the nslookup command multiple times to see if it returns inconsistent results.
 
DNSFilter is disabled.


Screen Shot 2022-05-09 at 17.46.55.png



Later I'll remove the dnsmasq config and try the nslookup commands on my computer. But the fact that it also happens "half the time" on my iPhone makes me think this might not be the problem. It's weird.
 
How do you turn loopback on and off - is this setting in the GUI? Is it enabled OOTB?

With loopback enabled, I should be able to access an internal service using the domain name (WAN IP) from an internal device?

I also don't see the option "Enable DNS-based Filtering" in my RT-AC68P GUI. Where is that?
 
How do you turn loopback on and off - is this setting in the GUI? Is it enabled OOTB?

With loopback enabled, I should be able to access an internal service using the domain name (WAN IP) from an internal device?
You can't disable loopback. It's a function of the firewall, provided of course that you have the relevant port forwarding rules enabled.


I also don't see the option "Enable DNS-based Filtering" in my RT-AC68P GUI. Where is that?
Are you running Merlin's firmware?
 
Wowza! I guess I have not tried this since I bought my ASUS. This didn't work on my old router, and I didn't expect loopback to work on consumer-grade boxes. Nice.

Not using Merlin.
 

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