DNS issue while tethered

[x86]

Hello All,
I have been working on getting USB tethering working on my Asus RTAX86U (Merlin 386.3.2) with an Android phone (USB) and have run into an issue. Everything appears to be working for wireless clients, though for wired clients (connected to the router itself) they have a strange issue where they cannot resolve IP addresses. Everything else appears to work correctly, I can ping IP addresses local and on the Internet though cannot resolve using the router as the DNS server. If I change the DNS server on a computer to a different DNS server (say 8.8.8.8) I can then resolve but not using the router, if I remove the tether everything works as expected. I would prefer to keep using the router as the DNS server if possible so I'm wondering if there has been a step I have missed or if there is something else going on I can look at? Any help on this is greatly appreciated, thanks!

 

[dosborne]

I'm guessing, but it sounds like your router is still trying to use whatever DNS server it is configured to use but can't reach it once the link is switched. Are you using a public DNS for the router now or a private one? How are you initiating the switch?

 

[x86]

That is the interesting part - if I configure the router for say 8.8.8.8 normally it works, when tethered it doesn't for the wired clients, though testing DNS resolution on the router itself works, also setting 8.8.8.8 on the clients works (by setting it manually), also setting it as an option for DHCP clients that works, it just appears to fail for wired connections, the kicker is that wireless clients do not have this issue, they can use the router for name resolution without any issues. It's suspect there might be an issue with how the wired connections are versus the wireless while tethered. I ran out of time today trying to track that part down though.

I'm using public DNS, I've tried Google, CloudFlare and OpenDNS servers with the same results.

Are you asking about how I am switching between the normal connection and tethered? If so, I'm just connecting the phone and disconnecting the wire to the Internet. Everything is setup for automatic fail-over which appears to be working correctly. let me know if that helps or if I read that incorrectly, thanks!

 

[dosborne]

Are you asking about how I am switching between the normal connection and tethered? If so, I'm just connecting the phone and disconnecting the wire to the Internet. Everything is setup for automatic fail-over which appears to be working correctly. let me know if that helps or if I read that incorrectly, thanks!

Indeed, yes. That is what I was asking.
The only thing I can suggest it examining the dynamic configuration on the clients to see what they are obtaining and resolving. Sounds like a route is not updating during the failover implementation. Someone else here can probably help you more with this.

 

[x86]

Not a problem, I checked the DHCP client side configuration, all looks normal - DNS server points to the router IP address. Also tried to clean/refresh lease, same IPs and results - I'm suspect of how the router is passing DNS resolution to the wired clients, I'll have to see if I can't troubleshoot that further but from the looks of it the DNS servers are reachable it is just the router not routing them correctly for the wired hosts. I'll have to dig up more on this the next time I can test. Thanks for the suggestions though, it is always helpful to have another set of eyes looking at this.

 

[Morris]

If you have all the advanced DNS features disabled and it's not working, the easy fix would be to have the DHCP server give out the DNS servers. You can find the settings you need on the LAN tab on the left and then the DHCP tab on the top. Fill in DHCP server 1 and DHCP server 2. Set Advertise routers IP in addition to user specified DNS servers to no.

Morris

 

[x86]

If you have all the advanced DNS features disabled and it's not working, the easy fix would be to have the DHCP server give out the DNS servers. You can find the settings you need on the LAN tab on the left and then the DHCP tab on the top. Fill in DHCP server 1 and DHCP server 2. Set Advertise routers IP in addition to user specified DNS servers to no.

Morris

Hi Morris,
That will be my fail-back procedure, though I'm trying to avoid this at the moment as I do want to keep using the router as the DNS server as it helps provide internal resolution for some resources on my network and since the wireless clients don't seem to have a problem I'm thinking there might be a fix for this. I'm going to dive more into the router the next time I can test and see what is going on.