[Bug 1728445] [NEW] DNS not working for IPv6-only host names when using Miredo

[Martin Rosenau]

Public bug reported:

When IPv6 is only available using "miredo" (I don't know about the case
of native IPv6) "systemd-resolve" seems not to query for AAAA entries
when AF_UNSPEC or simply a NULL pointer is passed to getaddrinfo().

This has the effect that tools that support both IPv4 and IPv6 and use
AF_UNSPEC or NULL will simply fail to connect IPv6-only servers when the
name has to be resolved via DNS.

(The problem was occurring with the Firefox web browser.)

(The AAAA record is however queried if AF_INET6 is explicitly passed to
that function.)

A possible quick fix is to modify the /etc/nsswitch.conf:

  Before: "hosts: ... resolve [!UNAVAIL=return] dns"
  After: "hosts: ... resolve dns"
  Or even remove "resolve" completely: "hosts: ... dns"

However it would be better to create the possibility to configure how
the system should behave in the case of AF_UNSPEC:

- Only ask for the A record
- Only ask for the AAAA record
- Ask for both, prefer A
- Ask for both, prefer AAAA

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

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https://bugs.launchpad.net/bugs/1728445

Title:
  DNS not working for IPv6-only host names when using Miredo

Status in resolvconf package in Ubuntu:
  New

Bug description:
  When IPv6 is only available using "miredo" (I don't know about the
  case of native IPv6) "systemd-resolve" seems not to query for AAAA
  entries when AF_UNSPEC or simply a NULL pointer is passed to
  getaddrinfo().

  This has the effect that tools that support both IPv4 and IPv6 and use
  AF_UNSPEC or NULL will simply fail to connect IPv6-only servers when
  the name has to be resolved via DNS.

  (The problem was occurring with the Firefox web browser.)

  (The AAAA record is however queried if AF_INET6 is explicitly passed
  to that function.)

  A possible quick fix is to modify the /etc/nsswitch.conf:

    Before: "hosts: ... resolve [!UNAVAIL=return] dns"
    After: "hosts: ... resolve dns"
    Or even remove "resolve" completely: "hosts: ... dns"

  However it would be better to create the possibility to configure how
  the system should behave in the case of AF_UNSPEC:

  - Only ask for the A record
  - Only ask for the AAAA record
  - Ask for both, prefer A
  - Ask for both, prefer AAAA

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