[Bug 1861884] [NEW] qemu socket multicast not working

[Maarten]

Public bug reported:

Running two qemu vms on the same socket multicast address:

  qemu-system-x86_64 -m 2048 -smp 2 -serial mon:stdio
    -display none -vga none
    -nodefaults -accel hax
    -netdev user,id=mynet0
    -device virtio-net-pci,netdev=mynet0
    -netdev socket,id=vlan,mcast=239.192.0.1:1235
    -device virtio-net-pci,netdev=vlan
    -device virtio-rng-pci
    -drive file=worker.qcow2,if=virtio
    -drive file=cloud-init.iso,format=raw,if=virtio

The two machines have a static ip on the socket network interface,
192.168.100.11 and 192.168.100.12, but are unable to reach each other.

Result when using ping command

  PING 192.168.100.11 (192.168.100.11) 56(84) bytes of data.
  From 192.168.100.12 icmp_seq=1 Destination Host Unreachable
  From 192.168.100.12 icmp_seq=2 Destination Host Unreachable
  From 192.168.100.12 icmp_seq=3 Destination Host Unreachable

Is there additional configuration necessary on macos? Does this only
work on Linux? Is there additional configuration required inside of the
guest OS?

guest OS: Debian 10 (Buster)
host OS: macOS 10.15.2
qemu: 4.2.0

** Affects: qemu
     Importance: Undecided
         Status: New

** Description changed:

  Running two qemu vms on the same socket multicast address:
  
-   qemu-system-x86_64 -m 2048 -smp 2 -serial mon:stdio -display none -vga none
-     -nodefaults -accel hax
-     -netdev user,id=mynet0
-     -device virtio-net-pci,netdev=mynet0
-     -netdev socket,id=vlan,mcast=239.192.0.1:1235
-     -device virtio-net-pci,netdev=vlan
-     -device virtio-rng-pci
-     -drive file=worker.qcow2,if=virtio
-     -drive file=cloud-init.iso,format=raw,if=virtio
+   qemu-system-x86_64 -m 2048 -smp 2 -serial mon:stdio
+     -display none -vga none
+     -nodefaults -accel hax
+     -netdev user,id=mynet0
+     -device virtio-net-pci,netdev=mynet0
+     -netdev socket,id=vlan,mcast=239.192.0.1:1235
+     -device virtio-net-pci,netdev=vlan
+     -device virtio-rng-pci
+     -drive file=worker.qcow2,if=virtio
+     -drive file=cloud-init.iso,format=raw,if=virtio
  
  The two machines have a static ip on the socket network interface,
  192.168.100.11 and 192.168.100.12, but are unable to reach each other.
  
  Is there additional configuration necessary on macos? Does this only
  work on Linux?
  
  guest OS: Debian 10 (Buster)
  host OS: macOS 10.15.2
  qemu: 4.2.0

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https://bugs.launchpad.net/bugs/1861884

Title:
  qemu socket multicast not working

Status in QEMU:
  New

Bug description:
  Running two qemu vms on the same socket multicast address:

    qemu-system-x86_64 -m 2048 -smp 2 -serial mon:stdio
      -display none -vga none
      -nodefaults -accel hax
      -netdev user,id=mynet0
      -device virtio-net-pci,netdev=mynet0
      -netdev socket,id=vlan,mcast=239.192.0.1:1235
      -device virtio-net-pci,netdev=vlan
      -device virtio-rng-pci
      -drive file=worker.qcow2,if=virtio
      -drive file=cloud-init.iso,format=raw,if=virtio

  The two machines have a static ip on the socket network interface,
  192.168.100.11 and 192.168.100.12, but are unable to reach each other.

  Result when using ping command

    PING 192.168.100.11 (192.168.100.11) 56(84) bytes of data.
    From 192.168.100.12 icmp_seq=1 Destination Host Unreachable
    From 192.168.100.12 icmp_seq=2 Destination Host Unreachable
    From 192.168.100.12 icmp_seq=3 Destination Host Unreachable

  Is there additional configuration necessary on macos? Does this only
  work on Linux? Is there additional configuration required inside of
  the guest OS?

  guest OS: Debian 10 (Buster)
  host OS: macOS 10.15.2
  qemu: 4.2.0

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