virtualbox.org

All my VMs guest are defined with network adapter "NAT"
Until recently, they used to access Internet without any problem.

Since today, I'm no more able to access Internet, and this from ANY of my VMs guest, either Windows (XP, 7 and W10) or Linux (LinuxMint)
Since the issue is present with all my guest, it obviously comes from the Host, and not from the guests.

If I check network parameters on the different guests, eveything seems to be OK, and actually the VMs says they access to Interne. But any try fails.
If I change the network adapter to "Bridge", access to internet works fine. (and if I go back to "NAT", the VMs says again it access to Internet, but actually any try fails again.)

The Host is a W10-1909 Pro.
I did'nt do (at least conciously...) any modification to my Host, EXCEPT the fact that I loaded yesterday the monthly (March 20) windows update.
I don't say that my issue is linked to this update (and I woud be very surprised if it was), but it's a fact that last time my guest were succesfully accessing Internet was BEFORE this montlhy windows update.

I used to run Vbox 6.1.2, but I just upgraded to 6.1.4 (hoping it would solve the issue, but unfortunately no change)

Any idea, in particular of what to check into the host ?

Too vague. Please pick one guest to talk about and provide a VM log. With the VM fully shut down, right click it in the GUI. Select "Show Log" and save "VBox.log" (no other file) to a zip file. Attach the zip here.

Here is the file.
The guest is a W10-1909 64 bits
I stopped the guest, then restarted it and eventually stopped it before getting VBox.log file attached.

Thanks in advance for your help.
Laurent

00:00:02.957679 Guest OS type: 'Windows7_64'
...
00:00:03.001338 Name <string> = "W7 migré W10" (cb=14)

Windows 10 requires that you use the Windows 10 template, not Windows 7. I don't see how you even got the VM to boot without this.

00:00:02.854316 Host RAM: 8073MB (7.8GB) total, 4405MB (4.3GB) available
...
00:00:03.001343 RamSize <integer> = 0x0000000100000000 (4 294 967 296, 4 096 MB, 4.0 GB)
00:00:03.001648 VRamSize <integer> = 0x0000000001b00000 (28 311 552, 27 MB)

No way this host can afford 4GB for a VM. Reduce to 2GB, and increase graphics RAM to 128MB.

00:00:15.614880 VMMDev: Guest Additions information report: Version 6.0.6 r130049 '6.0.6'

Best update the GAs too.

Let's see where you are after that.

Hi mpack,
thanks for answering.

I did what you asked for (and attached corresponding Vbox.log), but this didn't change anything, and I'm not surprised at all of that since I cannot see any link between my issue and what you mentioned (but since I'm asking for help, obviously I begin by doing what helper ask ! )

First of all, let me remind you that
- All my guests have the same symptom, while they do not have the same parameterization, and are not even of the same OS
- All my guest were working fine 1 or 2 weeks ago, and have all stopped to access internet, while I didn't change anything to their parameterization. The only change between "before" (internet access OK) and "after" (no internet access) is the March 20 WU of host.

Now, my comments on your proposals themselves :

1) The VM we are currently looking at has been originally created as a Win7 guest. And afterwards upgraded, using native Windows process to W10. This explain why it was based onto W7 template. How could we run such an upgrade if there were any incompatibility between these templates ?
Nevertheless, I updated it, and now, it is based on W10 template.

2) I cannot understand why my host, with 8GB memory, couldn't provide 4 GB (ie. half of hosts ram) to a guest ??? And actually, when the guest is running with 4GB, free memory remains on the host (~ 650MB)
Nevertheless, I reduced to 2GB (and increased graphics to 128MB)

3) On your 3rd bullet, I fully agree : As I mentioned in my initial post, I got the issue running VBox 6.1.2, and when I upgraded to 6.1.4, hoping it would fix the issue, I should (but I missed...) upgrade also GuestAdditions. It's now done.

Thanks to have a look on the new log attached... and good ideas to propose to fix my issue

More and more strange and quite un-understandable behaviour :

I launch the guest. Network adapter is defined as NAT
In the guest, I launch Firefox.
As mentioned in my initial post, I am unable to access any website (Firefox answers "Unable to connect" or something like that. Actually in french "Impossible de se connecter au serveur à l'adresse ..." )

Without closing Firefox (nor, of course, the guest VM), I switch network adapter to mode "Bridge"
Wait a few seconds connection establish
From Firefox, I become able to access to any Website

Up to now, nothing more "strange" than what I have already said in my initial post (why in Bridge and not in NAT ?)

But if, without closing Firefox, I switch back network to mode NAT, and wait a few seconds connection establish
From this pre-existing Firefox, I remain able to connect to any website. and this indefinitely.
But if I close Firefox, and restart it, I am no more able to access websites from any new Firefox Process !!! Again : "Unable to connect"....

And on the other hand, behaviour is not the same with Internet Explorer !!!
With IE, when network adapter is set to NAT mode, no access. If set to "Bridge", normal access to Web. Up to now, same behavior than with Firefox
But when set back network adapter to NAT, even currently running IE loses its web access, while in such a situation, as described above, FireFox continued to access Web .....

Actually, behaviour with IE seems quite "normal" : Access or No-acces to web depends only on NAT vs. Bridge. It doesn't explain why it works in Bridge and not in NAT, but it's somewhere consistent.
While with Firefox, it looks like something (what?) "opened a door" while network was in Bridge mode that remained open even when returned back to NAT mode.
But this "something" was linked to current Firefox process, and not "available" to a new process ????

And to make Strange even more strange, I have this behaviour in one of my guest VM, and NOT on another one (both being W10 guests...)

I'm afraid I become foolish
Maybe a Coronavirus impact ?

I have eventually found the issue !

This issue exists as soon as the DNSCache service is deactivated on host.
After reactivating it, everything works fine again, and Internet access is OK whetever "NAT" or "Bridge" adaptor (provided, of course, that the host itself has access to Internet....)

Deactivation of this service shouldn't have impact, since the only "drawback" of disabling this service should be a negative impact on performance (see https://docs.microsoft.com/en-us/window ... de-caching ), "cost to pay" to increase security.
Nevertheless, there is also this VERY NEGATIVE impact on VirtualBox. Maybe a bug of VirtualBox ?

Since it took me a while before understanding problem's origin, it could be interesting (for other users...) to store this information in a FAQ relative to "Prerequisites".
I don't know if such a FAQ exist, and if yes, where it is, but is a moderator reads me, and if such a FAQ exists, please add this new topic :

VirtualBox on Windows host requires that the DNSCache service is active on Host

And maybe a little add in Documentation would be great also... or a fix if it's actually a bug.

I had a similar situation just now (installed major update for my Windows 10 Pro and internet on the guest - Ubuntu 20.04 - stopped working). Thanks for your work it had helped me a lot.

However for me the DNS Client Service on my host Windows 10 Pro is always enabled it seems. I cannot change it or even restart it. What helped me was changing to a bridged connection, changed the adapter to a different one, then changed it back and the internet on the guest machine is back.

It seems I have to do this everytime I boot the guest machine so I will definitely investigate further what is causing it and will post later my finding in this thread.