VirtualBox host-only adapter keeps getting set to an invalid configuration, which breaks multicast.

[Fishscene]

Greetings!

OS: Windows 10 Pro x64 VirtualBox: 6.1.8r137981(Qt5.6.2)

The "VirtualBox Host-Only Network" adapter in Windows keeps getting set to an invalid state. When virtualbox is first installed, it populates the IPv4 IP address and DNS server. I also have to manually set the "Automatic Metric" to something like 800 as leaving it set to automatic breaks Multicast packets.

Every so often, I'll find I can't join a Multicast stream. Checking the settings in the "VirtualBox host-only network" adapter reveals:

• IP address/Subnet/Gateway are still set to manual, but are blank.
• DNS server is set to manual, and is completely blank
• Automatic Metric is set to automatic.

If I set the metric back to 800 and click ok, I get a message saying the IP address needs to be specified.

I have absolutely no idea what keeps changing the network properties for this adapter and setting it to an invalid state.

[Fishscene]

The program I use to listen in on multicast may be a factor here. I use VLC.

I found this post about VLC behavior when listening for Multicast packets: ​https://forum.videolan.org/viewtopic.php?t=78872 Specifically "The VLC player, as I have found, uses first ip address in the stack. Hence, we must push up the appropriate ip to high position by change its metric to lower value."

If the host-only adapter is somehow in the stack above the physical network adapter(even if it's the same metric), VLC may be defaulting to the host-only adapter.

[Fishscene]

It appears that at some point in the past, I had created a 2nd host-only network, and it was configured as: IPv4 Address: 0.0.0.0 IPv4 Network Mask: 0.0.0.0

The settings for this were stored somewhere in a vbox config file and thus persisted after uninstalling/re-installing Vbox.

Uninstall/Re-install Vbox would create 1 host-only adapter. After launching Vbox, the 2nd host-only adapter would be created. This was the adapter that I would manually set the administrative distance for and kept getting overwritten (by vbox configuration file upon launch).

I went to File > Host Network Manager and deleted the 2nd Host-only adapter (the option to delete it in Windows was grayed out).

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I will point out that after deleting the adapter, I was curious if vbox would let me create the invalid adapter again with the same settings. It does not. I'm wondering if I somehow created this adapter a few versions ago and it just carried over as vbox was upgraded. My specific scenario appears to be impossible to recreate. Well done vbox team. Well done. :)

I also want to give a shoutout to klaus-vb on IRC for working with me on this.

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For now, it appears we've identified what is changing the network adapter (bad config carried over from older installation of vbox.).

However, the original issue remains in that upon reboot of my computer, Multicast stops working.

Non-working state after reboot: netstat -nr Network Destination Netmask Gateway Interface Metric 192.168.56.1 255.255.255.255 On-link 192.168.56.1 281

Working state after setting metric to "800": netstat -nr 192.168.56.1 255.255.255.255 On-link 192.168.56.1 1056

Re-enabling automatic metric still allows Multicast traffic through: netstat -nr 192.168.56.1 255.255.255.255 On-link 192.168.56.1 281

I compared the output of the non-working netstat -nr (Left) and the working netstat -nr (Right). Both are set to automatic metric. (Diff between non-working and working netstat -nr.png)

[Fishscene]

Depicts bad host-only adapter settings that as of this Vbox version, is impossible to create. This was leftover from an older forgotten configuration.

[Fishscene]

Fresh reboot, multicast not working for VLC (left). After setting manual metric to 800, then back to automatic, I'm still receiving Multicast packets (right)

[Fishscene]

I have made no changes since the last post - other than to shut down my computer last night and turn it on again this morning. Multicast appears to still be working perfectly (Automatic metric is ticked).