Router Blocks Access To Single Site, Only On Selective Devices

Question

I have an ASUS RT-AC66U router and it's been functioning properly for the last year or so.

Then yesterday, I suddenly began experiencing a sporadic issue where a certain website couldn't be loaded.

The odd thing is that I can load the site from 2 of my 8 devices which are also connected to this router.

The site is actually my own and is hosted on a shared hosting server. None of the sites that point to that host are loading.

The only change that I can think of that would have caused this is when a week ago I needed a switch to connect multiple devices to the LAN (connected to the router) and so I hooked up an old DIR-655 router and disabled everything to have it act as a switch. It should be noted though that this was done a week ago, and the issue didn't come up until yesterday.

What I've tried so far:

• ran traceroute to the domain on the ASUS router: it hung at hop 20
• ran tracert on a Windows 10 machine and it got a few hops further than the router
• pinging on all devices, which always receives a successful reply
• spoofing the MAC address of a few devices on the router and powercycled the modem (read that on a forum somewhere): didn't work
• connecting directly to the modem. This always solves the problem which is what makes me believe that the issue is with the router
• connecting the router as a client through an OpenVPN connection: still didn't work (this one is odd to me)
• connecting to the FTP port of the website's domain. This worked!
• connecting explicitly through HTTPS (also tried wget through port 443): didn't work
• removing the DIR-655 from the whole setup: didn't work

Also to note, every time I made changes I flushed the dns on whatever device I was testing and rebooted the router.

The 2 devices on which the site DOES load are a Samsung cellphone and a laptop running Windows 7.

The other 2 cellphones, the raspberry pi, an Android tablet, a Windows 10 PC and a server running Ubuntu-Server are all unable to load the site.

Any ideas?

Edit (Additional Info):

• The devices that load the site will fail if I'm performing a POST action. (One of the things I use the site for is to update some personal agenda items. As soon as I click "Save" which performs a POST request, the site hangs. But then I can go back and see the site)
• I know that the devices aren't just loading a cached version of the webpage either because I've erased the cache and did hard refreshes on the pages... etc.
• An odd thing happened about a month ago which seems somewhat related now that I think about it: When I was loading the same site from my cellphone, but through my mobile data (I was out and about), it just hung up and gave me a "site took too long to respond" error like I'm getting on these devices now. And to further add to that oddity, that's the cellphone that works when connected to the ASUS router, but as soon as I disconnect and go on Cell Data, it hangs.

Answer 1

I hope this helps someone else who runs into this issue.

My problem was finally solved with an option in the Tomato firmware.

There is likely a way to do this without installing the Tomato software, but I do not have knowledge on where the option is in the stock ASUS firmware.

The Fix:

The option that fixed it all was setting the Route Modem IP to the address of the Modem/Router that comes with the ISP. In my setup, I connect this ISP modem/router to the WAN port of my ASUS router and disable everything on that ISP router (like DHCP etc...).

For my specific case, the modem's IP (the IP address I use to get to it's web interface) was 192.168.0.1. So I set that in the text box.

I was literally just trying every option and meticulously resetting everything in between each attempt. But as soon as I changed that option, every device was suddenly able to access the site.

I apologize for not being able to provide an explanation of why this worked, although I can confirm that setting that option back to Disabled suddenly breaks everything again.