[Bug 1865474] Re: sysytemd-resolved automatically use an ipv6 dns server on lan

[Marc Deslauriers]

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Title:
  sysytemd-resolved automatically use an ipv6 dns server on lan

Status in systemd package in Ubuntu:
  New

Bug description:
  lsb_release -rd
  Description:	Ubuntu Focal Fossa (development branch)
  Release:	20.04

  i installed focal from the netboot version mini.iso.

  i encountered some problem on dsn configuration and i found that
  systemd-resolved was using an ipv6 dns address

  this is my netplan configuration:

  network:
    version: 2
    renderer: networkd
    ethernets:
      ens3:
        addresses:
          - 192.168.1.1/24
        gateway4: 192.168.1.212
        nameservers:
            search: [xxx.com]
            addresses: [192.168.1.191, 192.168.1.206]

  this is the output of "systemd-resolved --status"

  Global
         LLMNR setting: no
  MulticastDNS setting: no
    DNSOverTLS setting: no
        DNSSEC setting: no
      DNSSEC supported: no
            DNSSEC NTA: 10.in-addr.arpa
                        16.172.in-addr.arpa
                        168.192.in-addr.arpa
                        17.172.in-addr.arpa
                        18.172.in-addr.arpa
                        19.172.in-addr.arpa
                        20.172.in-addr.arpa
                        21.172.in-addr.arpa
                        22.172.in-addr.arpa
                        23.172.in-addr.arpa
                        24.172.in-addr.arpa
                        25.172.in-addr.arpa
                        26.172.in-addr.arpa
                        27.172.in-addr.arpa
                        28.172.in-addr.arpa
                        29.172.in-addr.arpa
                        30.172.in-addr.arpa
                        31.172.in-addr.arpa
                        corp
                        d.f.ip6.arpa
                        home
                        internal
                        intranet
                        lan
                        local
                        private
                        test

  Link 2 (ens3)
        Current Scopes: DNS
  DefaultRoute setting: yes
         LLMNR setting: yes
  MulticastDNS setting: no
    DNSOverTLS setting: no
        DNSSEC setting: no
      DNSSEC supported: no
    Current DNS Server: fe80::6670:2ff:feb5:d9c8
           DNS Servers: 192.168.1.191
                        192.168.1.206
                        fe80::6670:2ff:feb5:d9c8
            DNS Domain: xxx.com

  --
  as you can see systemd is using the ipv6 dns server.

  i found that such ip was the address of my openwrt wifi router. dnsmasq is disabled for ipv4 lan interface on the router and i never configured an ipv6 network. Anyway i disabled all the ipv6 dnsmasq feature on the router and after a restart this fixed the problem.
  But i think that this is a bug.
  In my netplan i never configured an ipv6 dns nor a ipv6 network; furthermore none of my other ubuntu bionic servers showed such a behaviour.
  Also another focal netboot installation i made three weeks ago didn't show this problem.

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