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In a mess with DNS

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alan6854321

Senior Member
I seem to have got myself into a complete mess, there's a couple of similar threads here, but none help me.

I had everything running fine, main WiFi and guest2 Wifi are split with different SSID's for 2.4G & 5G with IoT stuff on the guest network.
I have two piHoles running DNS, their network addresses are in the WAN DNS Setting's fields on the "WAN - Internet Connection" page

Then I thought I'd install YazFi so I could tell which IoT device was making DNS requests. I installed it, realized the clients wouldn't appear in the network map page anymore, decided I wouldn't bother and uninstalled it.

I have never been able to get things working again. The guest network seems to be OK but I get strange results if I connect to 2.4G main network and 5G main network.

It seems that sometime (almost at random), DNS queries resolve to odd addresses, e.g. "bbc.co.uk" should resolve to "151.101.128.81", but sometimes gets an address like "198.18.1.73". It's inconsistant and random. I get different results between 2.4G & 5G. The problems only seem to affect my two Windows 10 P/C's, Android phones seem unaffected.

I have tried a factory reset from UI on the router, including formatting JFFS and rebuilding the router by hand (not from saved config)
I have also rolled back the P/C's using Macrium to a date when they were working, I've rebooted the PiHoles and flushed their caches.

Any ideas?

It's an RT-AC86U running Merlin 386.1_2
 
Last edited:
Is your ISP Plusnet?

 
Then this appears to be a "feature" of the Plusnet modem.

But why did it work fine until I tried to install YazFi,
And why am I unable to get back to the state I was in before?
 
Then this appears to be a "feature" of the Plusnet modem.

AHA - Lightbulb moment!!!

I use my old Plusnet router (Technicolor TG562n) as a Wifi repeater over powerline.
I just switched it off and everything works again.
It would explain why the guest network was fine (they can't 'see' it).

Is it advertising a DNS server that is sometimes catching queries?
Is that possible?

Is it possible to block DNS access to it, as it's really useful to run it.
 
I have no experience of the Technicolor but it sounds like it might have a DHCP server enabled which would conflict with the Asus' DHCP server, potentially hijacking clients and redirecting them to itself.
 
Is there anyway to put a route in to stop anything accessing it's DNS port e.g. 192.168.1.35:53 ?
 
No, because it's not a routing issue. You need to disable it's DHCP server, assuming that's the cause of the problem.
 
No, because it's not a routing issue. You need to disable it's DHCP server, assuming that's the cause of the problem.

I already disabled DHCP on it, did you mean DNS server?
Because I don't see anyway to disable that.
 
No I did mean DHCP server because that is the way a client is told what DNS server to use. DNS servers do not advertise themselves. You could have numerous DNS servers on your LAN but they will only be used if a client is told to do so.

It's possible that the Technicolor is not "just a repeater" but is behaving more like a router and intercepting DNS requests from its clients. From a client connected to the repeater issue an ipconfig /all command and check the IP addresses.
 

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