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

[Dimitri John Ledkov]

Digging into this, there appears to be intent to support such DNS
servers. E.g.:

https://github.com/systemd/systemd/commit/2817157bb705e0f3e9ad4a83246a80d026866be3

However, need to check if all fe80:: dns servers are properly qualified
and have the ifindex set on them.

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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:
  Confirmed
Status in systemd source package in Artful:
  Confirmed

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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