DNS Leak despite forcing clients to use local resolver?

Technical Support for Routers
1

I have “Override DNS Settings for All Clients” enabled with AdGuardHome installed but I often see some clients connecting to 8.8.8.8:53 still in Luci > Status > Realtime Graph > Connections. I tried many firewall traffic rules to block 8.8.8.8, but nothing seem to work. I am on Convexa-S btw, latest firmware.

I also tried adding the following to custom rules but nothing

iptables -I FORWARD --destination 8.8.8.8 -j REJECT
iptables -I FORWARD --destination 8.8.4.4 -j REJECT
iptables -I FORWARD --destination 2001:4860:4860::8888 -j REJECT
iptables -I FORWARD --destination 2001:4860:4860::8844 -j REJECT

I also tried the following traffic rules:
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2

If you want to reject router itself generated traffic, it should be:

iptables -I OUTPUT --destination 8.8.8.8 -j REJECT
iptables -I OUTPUT --destination 8.8.4.4 -j REJECT

Are you using firmware 3.216?

3

I was on 3.215. Anyways, I did the mistake of confusing the router traffic and using FORWARD rules. I think everything is working as I intended now. Thanks.