OpenWrt DNS filter

Hi,

if i set the dns filter in WAN Use custom DNS servers works ok,
but if set on LAN -> DHCP Server -> DHCP-Options it flaws, and can access adult content.

i prefer the last one which advertises to clients.

Take a look here: https://openwrt.org/docs/guide-user/firewall/fw3_configurations/fw3_parent_controls

You had it right putting the DNS filtering resolver in WAN. Now intercept the DNS to keep devices from bypassing the router.

These are different cases. In the first one you are using an upstream resolver to forward the queries and advertise OpenWrt as DNS to the lan hosts. In the second you advertise an upstream resolver to the lan hosts. In both cases that can be bypassed and you need to make sure that lan hosts won't be allowed that.