Dear Merguin!
1. Check whether your product is a customized product provided by the carrier. If so, then your DNS function may not be disabled. Contact the carrier and apply for replacing the firmware or device to enable this function.
2. If no, configure the device as a user with higher permissions.
3. If the fault persists, you can change the node in the VSA profile of the U2000 to configure the DNS service for the ONT.
</LANEthernetInterfaceConfig>
<LANHostConfigManagement X_HW_DHCPOption82Enable="0" X_HW_PPPoEPITPEnable="0" X_HW_DNSList="8.8.8.8">
<IPInterface MaxNumber="2" NumberOfInstances="0"/>
</LANEthernetInterfaceConfig>
<LANHostConfigManagement X_HW_DHCPOption82Enable="0" X_HW_PPPoEPITPEnable="0" X_HW_DNSList="8.8.8.8","9.9.9.9">
<IPInterface MaxNumber="2" NumberOfInstances="0"/>
Find the node and manually add X_HW_DNSList="8.8.8.8".
If the product is customized by a carrier, the node is changed and cannot be found.
Thanks!