If you want to run your own recursive DNS server, you must find upstream servers that are authoritative for the dn42 zones.

You may use some servers listed in the table of anycast servers, or just use 172.22.119.129 and 172.22.119.139 (ns{1,2}.fritz.dn42).

Configuration

Unbound

Configuration for unbound.conf

server:
        local-zone: "22.172.in-addr.arpa." nodefault
        local-zone: "23.172.in-addr.arpa." nodefault

stub-zone:
        name: "dn42"
        stub-prime: yes
        stub-addr: 172.22.119.139
        stub-addr: 172.22.119.129

stub-zone:
        name: "22.172.in-addr.arpa"
        stub-prime: yes
        stub-addr: 172.22.119.139
        stub-addr: 172.22.119.129

stub-zone:
        name: "23.172.in-addr.arpa"
        stub-prime: yes
        stub-addr: 172.22.119.139
        stub-addr: 172.22.119.129