DNS Cache Issues on R6220

[nerdburt]

We have been unsuccessful in getting an iPhone 11 working with WiFi with our R6220 WiFi router, with iOS 15.4.  When surfing the Internet with the iPhone, it is clear that DNS is not working properly.   We are using the latest version of firmware, V1.1.0.112_1.0.1 and have tried downgrading back several versions, with absolutely no improvement.  

From several tests done, it appears that the DNS cache is corrupting very badly as soon as the iPhone starts using WiFi.  I had nslookup running with queries before, during and after the iPhone is connecting.  When we move the iPhone over to cell data (expensive), the issue stops.  After a few minutes, DNS cache corrects itself.

Until this is resolved, we have major issues using our cell phone on WiFi.  Wondering if anyone else has found this issue, and any workarounds?  We may have to dump NetGear if this is not resolved and are quite disappointed.

Before using iPhone (app: Google News):

nslookup [using server192.168.1.1]

> cbsnews.com
Server: www.routerlogin.com
Address: 192.168.1.1

Non-authoritative answer:
Name: cbsnews.com
Addresses: 151.101.1.188
151.101.65.188
151.101.129.188
151.101.193.188

After using iPhone (app: Google News):

nslookup [using server 192.168.1.1]

> cbsnews.com
Server: www.routerlogin.com
Address: 192.168.1.1

DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
*** Request to www.routerlogin.com timed-out
> cbsnews.com
Server: www.routerlogin.com
Address: 192.168.1.1

DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
*** Request to www.routerlogin.com timed-out

[plemans]

what modem/gateway is the router connected to? 

Do you have IPv6 enabled? (if not, try it)

on the iphone, have you disabled the random ip/random mac option? 

Did you try a different dns provider like googles at 8.8.8.8 or 8.8.4.4

[nerdburt]

Yes, we tried different DNS providers to no avail, and IPv6.  Our provider does not carry IPv6 yet in this part of Canada, but we turned it on anyway, and no change.  Have not tried the MAC ramdomization, so will give it a whirl and report back.

[nerdburt]

We have done a few things,which seems to make the iPhone work a lot better.   

1.) Turn 'private address mode' off, also known as MAC randomization.

   https://www.techrepublic.com/article/how-to-manage-or-disable-mac-randomization-in-ios-and-ipados-14...

2.) Eliminated the port-forwarding that was turned on, as part of troubleshooting VoIP issues.   We had UDP port forwarding enabled for two ranges of ports, and deleted them both.

I have also noticed the performance of the router improves slightly with these changes.  I am assuming that the MAC randomization was putting the router into a bad state.    Will now monitor to see if this improvement stays.  Thanks for the idea.