[Bug 1641328] [NEW] Ordering of mdns4_minimal and resolve in /etc/nsswitch.conf causes mDNS lookups to fail

[Mark Tearle]

Public bug reported:

(See also libnss-resolve:amd64   231-9ubuntu1 amd64        nss module to
resolve names via systemd-resolved)


# fresh install of yakkety 

mtearle at liberation:/etc$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 16.10
Release:	16.10
Codename:	yakkety

# package details

mtearle at liberation:~$ apt-cache policy libnss-resolve
libnss-resolve:
  Installed: 231-9ubuntu1
  Candidate: 231-9ubuntu1
  Version table:
 *** 231-9ubuntu1 500
        500 http://mirror.rackspace.com/ubuntu yakkety-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     231-9git1 500
        500 http://mirror.rackspace.com/ubuntu yakkety/main amd64 Packages
mtearle at liberation:~$ apt-cache policy systemd
systemd:
  Installed: 231-9ubuntu1
  Candidate: 231-9ubuntu1
  Version table:
 *** 231-9ubuntu1 500
        500 http://mirror.rackspace.com/ubuntu yakkety-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     231-9git1 500
        500 http://mirror.rackspace.com/ubuntu yakkety/main amd64 Packages


# attempt to ping VM elsewhere on network with mDNS hostname

mtearle at liberation:/etc$ ping bazzavan.local
ping: bazzavan.local: Name or service not known

# can find both ipv4 and ipv6 addresses for the host

mtearle at liberation:/etc$ avahi-resolve-host-name bazzavan.local
bazzavan.local	fe80::a00:27ff:fea5:3f51

mtearle at liberation:/etc$ avahi-resolve-host-name -4 bazzavan.local
bazzavan.local	172.16.44.48

# can ping it

mtearle at liberation:/etc$ ping -c 1 172.16.44.48
PING 172.16.44.48 (172.16.44.48) 56(84) bytes of data.
64 bytes from 172.16.44.48: icmp_seq=1 ttl=64 time=0.265 ms

--- 172.16.44.48 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.265/0.265/0.265/0.000 ms

# original ordering

mtearle at liberation:/etc$ grep hosts /etc/nsswitch.conf 
hosts:          files resolve [!UNAVAIL=return] mdns4_minimal [NOTFOUND=return] dns

# go away and edit /etc/nsswitch.conf
# change ordering of resolve and mdns4_minimal

mtearle at liberation:/etc$ grep hosts /etc/nsswitch.conf 
hosts:          files mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns

# check mdns lookups now work, and it now pings

mtearle at liberation:/etc$ ping -c 1 bazzavan.local
PING bazzavan.local (172.16.44.48) 56(84) bytes of data.
64 bytes from 172.16.44.48 (172.16.44.48): icmp_seq=1 ttl=64 time=0.161 ms

--- bazzavan.local ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.161/0.161/0.161/0.000 ms


# check libnss-resolve is still doing its thing

mtearle at liberation:/etc$ ping -c 1 localhost.localdomain
PING localhost.localdomain(localhost (::1%1)) 56 data bytes
64 bytes from localhost (::1): icmp_seq=1 ttl=64 time=0.016 ms

--- localhost.localdomain ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.016/0.016/0.016/0.000 ms

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

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https://bugs.launchpad.net/bugs/1641328

Title:
  Ordering of mdns4_minimal and resolve in /etc/nsswitch.conf causes
  mDNS lookups to fail

Status in systemd package in Ubuntu:
  New

Bug description:
  (See also libnss-resolve:amd64   231-9ubuntu1 amd64        nss module
  to resolve names via systemd-resolved)

  
  # fresh install of yakkety 

  mtearle at liberation:/etc$ lsb_release -a
  No LSB modules are available.
  Distributor ID:	Ubuntu
  Description:	Ubuntu 16.10
  Release:	16.10
  Codename:	yakkety

  # package details

  mtearle at liberation:~$ apt-cache policy libnss-resolve
  libnss-resolve:
    Installed: 231-9ubuntu1
    Candidate: 231-9ubuntu1
    Version table:
   *** 231-9ubuntu1 500
          500 http://mirror.rackspace.com/ubuntu yakkety-updates/main amd64 Packages
          100 /var/lib/dpkg/status
       231-9git1 500
          500 http://mirror.rackspace.com/ubuntu yakkety/main amd64 Packages
  mtearle at liberation:~$ apt-cache policy systemd
  systemd:
    Installed: 231-9ubuntu1
    Candidate: 231-9ubuntu1
    Version table:
   *** 231-9ubuntu1 500
          500 http://mirror.rackspace.com/ubuntu yakkety-updates/main amd64 Packages
          100 /var/lib/dpkg/status
       231-9git1 500
          500 http://mirror.rackspace.com/ubuntu yakkety/main amd64 Packages



  # attempt to ping VM elsewhere on network with mDNS hostname

  mtearle at liberation:/etc$ ping bazzavan.local
  ping: bazzavan.local: Name or service not known

  # can find both ipv4 and ipv6 addresses for the host

  mtearle at liberation:/etc$ avahi-resolve-host-name bazzavan.local
  bazzavan.local	fe80::a00:27ff:fea5:3f51

  mtearle at liberation:/etc$ avahi-resolve-host-name -4 bazzavan.local
  bazzavan.local	172.16.44.48

  # can ping it

  mtearle at liberation:/etc$ ping -c 1 172.16.44.48
  PING 172.16.44.48 (172.16.44.48) 56(84) bytes of data.
  64 bytes from 172.16.44.48: icmp_seq=1 ttl=64 time=0.265 ms

  --- 172.16.44.48 ping statistics ---
  1 packets transmitted, 1 received, 0% packet loss, time 0ms
  rtt min/avg/max/mdev = 0.265/0.265/0.265/0.000 ms

  # original ordering

  mtearle at liberation:/etc$ grep hosts /etc/nsswitch.conf 
  hosts:          files resolve [!UNAVAIL=return] mdns4_minimal [NOTFOUND=return] dns

  # go away and edit /etc/nsswitch.conf
  # change ordering of resolve and mdns4_minimal

  mtearle at liberation:/etc$ grep hosts /etc/nsswitch.conf 
  hosts:          files mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns

  # check mdns lookups now work, and it now pings

  mtearle at liberation:/etc$ ping -c 1 bazzavan.local
  PING bazzavan.local (172.16.44.48) 56(84) bytes of data.
  64 bytes from 172.16.44.48 (172.16.44.48): icmp_seq=1 ttl=64 time=0.161 ms

  --- bazzavan.local ping statistics ---
  1 packets transmitted, 1 received, 0% packet loss, time 0ms
  rtt min/avg/max/mdev = 0.161/0.161/0.161/0.000 ms

  
  # check libnss-resolve is still doing its thing

  mtearle at liberation:/etc$ ping -c 1 localhost.localdomain
  PING localhost.localdomain(localhost (::1%1)) 56 data bytes
  64 bytes from localhost (::1): icmp_seq=1 ttl=64 time=0.016 ms

  --- localhost.localdomain ping statistics ---
  1 packets transmitted, 1 received, 0% packet loss, time 0ms
  rtt min/avg/max/mdev = 0.016/0.016/0.016/0.000 ms

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