[Bug 1642421] Re: qemu-system-x86_64: ipv6 and dns is broken with netdev user

[Thomas Huth]

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** Changed in: qemu
       Status: New => Incomplete

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Title:
  qemu-system-x86_64: ipv6 and dns is broken with netdev user

Status in QEMU:
  Incomplete

Bug description:
  Hi,

  dhcp inside qemu returns an ipv6 address as dns-server. However this is not
  working. If i replace it with the ipv4 address '10.0.0.2' dns is working
  again. I would expect that the qemu emulated dhcp server responds either an
  ipv4 configuration that is working or its dns server/forwarder listens on the
  ipv6 address returned by the emulated dhcp server.

  I used latest qemu from git (
  b0bcc86d2a87456f5a276f941dc775b265b309cf) and used the following
  commands:

  $ ./qemu-system-x86_64 -enable-kvm -M pc -device virtio-rng-pci -device
  virtio-net-pci,netdev=user.0 -drive file=buildenv.img,if=virtio,bus=1,unit=0
  -no-reboot -netdev 
user,id=user.0,hostfwd=tcp::5022-:22,hostfwd=tcp::7587-:7588
  -m 1024 -usb -nographic -smp 4

  buildenv.img is a debian jessie amd64 installation.

  Inside qemu the network is configured to use dhcp:

  $ cat /etc/network/interfaces
  allow-hotplug eth0
  iface eth0 inet dhcp

  $ ifconfig eth0
  eth0      Link encap:Ethernet  HWaddr 52:54:00:12:34:56
            inet addr:10.0.2.15  Bcast:10.0.2.255  Mask:255.255.255.0
            inet6 addr: fe80::5054:ff:fe12:3456/64 Scope:Link
            inet6 addr: fec0::5054:ff:fe12:3456/64 Scope:Site
            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
            RX packets:10 errors:0 dropped:0 overruns:0 frame:0
            TX packets:28 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:1000
            RX bytes:3215 (3.1 KiB)  TX bytes:3638 (3.5 KiB)

  $ cat /etc/resolv.conf
  nameserver fec0::3

  $ arp google.de
  google.de: Host name lookup failure

  $ strace -f arp google.de
  ...
  socket(PF_INET6, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 4
  connect(4, {sa_family=AF_INET6, sin6_port=htons(53), inet_pton(AF_INET6, 
"fec0::3", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) = 0
  poll([{fd=4, events=POLLOUT}], 1, 0)    = 1 ([{fd=4, revents=POLLOUT}])
  sendto(4, "\17\320\1\0\0\1\0\0\0\0\0\0\6google\2de\0\0\1\0\1", 27, 
MSG_NOSIGNAL, NULL, 0) = 27
  poll([{fd=4, events=POLLIN}], 1, 5000)  = 0 (Timeout)
  poll([{fd=4, events=POLLOUT}], 1, 0)    = 1 ([{fd=4, revents=POLLOUT}])
  sendto(4, "\17\320\1\0\0\1\0\0\0\0\0\0\6google\2de\0\0\1\0\1", 27, 
MSG_NOSIGNAL, NULL, 0) = 27
  poll([{fd=4, events=POLLIN}], 1, 5000)  = 0 (Timeout)
  close(4)                                = 0
  ...

  $ echo nameserver 10.0.0.2 > /etc/resolv.conf

  $ arp google.de
  google.de (216.58.208.35) -- no entry

  Note: I reported this bug also to debian: https://bugs.debian.org/cgi-
  bin/bugreport.cgi?bug=844566

  Regards,

    Manuel

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