[Bug 1718771] Re: Incorrect handling of link-local IPv6 DNS servers

[Dimitri John Ledkov]

Trying to reproduce this error:

I did:
$ lxc launch ubuntu-daily:artful
$ lxc exec relaxed-fly bash

Edited /run/systemd/network/10-netplan-eth0.network to become:
[Match]
Name=eth0

[Network]
DHCP=ipv4
DNS=fe80::307e:12ff:fec4:90ba

[DHCP]
UseMTU=true
RouteMetric=100
UseDNS=no

where fe80... address is the right address for the lxd host provided
dnsmasq.

Then I restarted everything:
$ sudo systemctl restart systemd-networkd systemd-resolved
$ systemd-resolve --flush-caches
$ ip link set dev eth0 down
$ ip link set dev eth0 up


# systemd-resolve --status eth0
Link 28 (eth0)
      Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
       LLMNR setting: yes
MulticastDNS setting: no
      DNSSEC setting: no
    DNSSEC supported: no
         DNS Servers: fe80::307e:12ff:fec4:90ba
          DNS Domain: lxd

# systemd-resolve google.com
google.com: 216.58.204.46%eth0
            2a00:1450:4009:80d::200e%eth0

-- Information acquired via protocol DNS in 26.2ms.
-- Data is authenticated: no

# host google.com
google.com has address 216.58.204.46
google.com has IPv6 address 2a00:1450:4009:80d::200e
google.com mail is handled by 30 alt2.aspmx.l.google.com.
google.com mail is handled by 10 aspmx.l.google.com.
google.com mail is handled by 40 alt3.aspmx.l.google.com.
google.com mail is handled by 50 alt4.aspmx.l.google.com.
google.com mail is handled by 20 alt1.aspmx.l.google.com.

Looks like a correct and valid responses to me.

This is with 234-2ubuntu12.1

Seems like it works correctly. I do wonder, if the bug here is that
systemd-resolved is not up yet, and is not responding on dbus and/or
over 127.0.0.53 at the point in time? I.e.
https://bugs.launchpad.net/ubuntu/artful/+source/systemd/+bug/1734167
which is currently awaiting verification.

I'll try to revert the docker.io upload you did locally; and rerun all
of these tests again; to see if i can make this work again.

** Changed in: systemd (Ubuntu)
       Status: Confirmed => Incomplete

** Changed in: systemd (Ubuntu Artful)
       Status: Confirmed => Incomplete

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https://bugs.launchpad.net/bugs/1718771

Title:
  Incorrect handling of link-local IPv6 DNS servers

Status in systemd package in Ubuntu:
  Incomplete
Status in systemd source package in Artful:
  Incomplete

Bug description:
  We've recently seen odd looking DNS failures on autopkgtest:
  https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-artful/artful/amd64/d/docker.io/20170921_065231_181b8@/log.gz

  This shows a fe80:: link-local IPv6 address as one of the DNS servers
  on the interface. That's because dnsmasq includes both the link-local
  and global addresses of its DNS server in the router advertisement.

  systemd-networkd appears to pick that up and send it to resolved,
  which includes it in its config but apparently doesn't know how to
  actually query it, leading to the failure above.

  
  This is racy because once DHCPv4 completes, the resolved config will then work properly again.

  
  I've confirmed that dnsmasq properly answers on all addresses:
    http://paste.ubuntu.com/25588197/

  
  I've uploaded a workaround for this issue as part of the docker.io package.

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