Scenario: The AR device works as a DHCP server and gateway for the LAN, using PPPoE uplink with automatic IP negociation.
Requirement: Import the DNS server list obtained from the uplink to the local DHCP IP pool for the LAN clients.
Issue: Normally there are 2 solutions used in this scenario, but they have limitations
1. Configure the DHCP server address manually into the IP pool.
This can cause issues for large deployments where the DNS server may not be the same on all devices.
2. Configure the AR to work as a DNS resolver with proxy or relay.
This opens the AR to "open resolver" attacks by responding to DNS requests from outside the LAN.
Using a traffic-filter to restrict DNS requests can have an impact on the forwarding performance.
Starting with Versions V2R8 and V2R9, it is possible to configure unnumbered dns-list parameters in the DHCP IP pool or DHCP server interface.
This allows the AR to import the DNS server obtained from the uplink into the DHCP IP pool allocated to the LAN.
IP address pool view:
dns-list unnumbered interface interface-type interface-number
dhcp server dns-list unnumbered interface interface-type interface-number
The interface-type interface-number should be the Dialer interface used for the PPPoE uplink.