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DNS fails for local devices when there is no WAN!

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Ive posted a lot of questions today apologies for that this is the last issue I'm having:
ASUS RT-AX88U on latest Merlin 3004.388.6

I use the router as the DNS server. I set hostnames for all my physical devices in DHCP, I set my domain name (mydomain.net) which is also my public domain name

Host name: router
RT-AX88U's Domain Name: mydomain.net (which is also my public domain name)

DCHP Server
Hide DHCP/RA queries : No
Default Gateway: <ROUTER IP ADDRESS>
DNS Server 1 <BLANK> but I did put in the router IP Address to test if it would work
Advertise router's IP in addition to user-specified DNS: No (But I also tried changing it to Yes)

in WAN:
Forward local domain queries to upstream DNS: No

Everything works great normally. I also have a lot of custom hostnames set in jffs/configs/dnsmasq.conf.add which point to my docker containers

But I discovered today if I unplug my wan port and have no WAN all of my local dns hostnames wont resolve and resolve back to like or something which isnt even an IP range in my network

it wont even resolve my router dns router.mydomain.net nor will it resolve any of my physical devices where the hostname is set in DHCP and it wont resolve any of my custom domains

and it affects every device on my network, windows machines, linux etc, as soon as I plug back in the WAN it will work again I dont even need to do an ipconfig /flush dns or renew or anything like that just repeat the nslookup and it works again!

So I just can't work out why it's doing this! the gateway and dns is set to my router ip so why should it matter I have no WAN the router should be handling the local hostnames inside my network without having to go outside to the WAN?

I dont have DNS Filtering turned on

Should I consider moving to something like pihole
Last edited:
If you don’t specify a dns server ie (cloud flare) or others then it will automatically point to the local dns server of your isp. If your WAN isn’t working then you don’t have internet access to point to any site outside of your network. Your router can cache dns sites locally or by using unbound, but they likely won’t resolve without internet. Dnssec, rebind protection check the sites signature is signed so it can’t verify the sites if no internet.View attachment 56589

I feel like I’m misunderstanding something.

Dns filter doesn’t really matter it’s just used to force clients to use a specific dns server or the routers. Some devices hardcode the dns server to say like googles dns servers and perhaps you want to use your own or a specific one that’s where you use dns filters. Some client devices use your routers dns as a secondary dns server which may not be adequate or preferred.

Your router isn’t really its own dns server it’s like a hub it just bridges to actual dns servers. (Unless you use unbound)

Don’t see why you need Pihole unless you want to replace your dhcp server and dns server with it. Diversion works much the same if your intent is ad blocking.

View attachment 56591
Under DNS if none or isp is specified then it will show your isp dns here. If you only provide 1 dns server or don’t set dns filter to router then it might show the first dns server being your isp dns server and the second being your manually set dns server.

View attachment 56592

Dns located under LAN - DHCP server simply tells your dhcp clients that this is where your local dns server is. Ie the router or say samba on a different server locally or externally in the internet.

View attachment 56593

This is because you have Administration - System > Enable WAN down browser redirect notice set to Yes.
Bingo! That was it thanks @ColinTaylor!

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