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

[Stéphane Graber]

Public bug reported:

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.

** Affects: systemd (Ubuntu)
     Importance: Undecided
         Status: New

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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:
  New

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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