virtualbox.org

saindo wrote:As for DNS server 10.0.2.3, during my 10 years' experience of Virtualbox on Ubuntu, I only noticed 10.0.0.1 as IP of host machine. I never made any modifications to this. It must be as default.

You NAT address scheme is somehow screwed up. And I was able to duplicate it! Here's what's going on.
- Your NAT adapter should get 10.0.2.15. It does. Good.
- Your gateway and DHCP server should be 10.0.2.2. It is. Good.
- Your DNS should be "borrowed" from your host. It isn't. It gets a non-existent 10.0.2.3. BAD.
- Changing ISPs (and routers) gets a secondary DNS address (221.131.143.69). Better.

Now, somewhere in your setup the "fixed" 10.0.2.3 DNS entry was introduced. Don't know how, don't know why. I was able to go to my network adapter properties, IP4 setup and instead of obtaining the DNS server automatically I assigned 10.0.2.3. Guess what; "No Internet access" message from the Windows 10 properties. So, search for changes to your setup and see how that 10.0.2.3 got inserted. And no, it is NOT the default...

The strangest thing is that, I do not have any problem with the native Win10 on another laptop with any ISP. I think this points to VirtualBox.

socratis wrote: Now, somewhere in your setup the "fixed" 10.0.2.3 DNS entry was introduced. Don't know how, don't know why. I was able to go to my network adapter properties, IP4 setup and instead of obtaining the DNS server automatically I assigned 10.0.2.3. Guess what; "No Internet access" message from the Windows 10 properties. So, search for changes to your setup and see how that 10.0.2.3 got inserted. And no, it is NOT the default...

I do not understand your statement actually. In my 4 guest OSes, including XP, Win7 and Win10, all DNS server is 10.0.2.3. This problem is only in Win10 guest. I never fiddle with this. So, for me, 10.0.2.3 is always the DNS by default here.

However, I found a practical work around. I still have another ISP-5, through Android hotspot again. Through this new ISP, I have no problem in Win10 under Ubuntu. And, the weird thing is that, after I start Win10 with this ISP with no problem, as long as I do not shut down the Win10 guest, I can switch my ISP to any other one ISP, without causing any problem. That is to say, the trick is start the guest Win10 with this ISP-5, get GOOD internet connection, then I can use any other ISP, I can hibernate/suspend the host Ubuntu and resume with any ISP with no problem. But if the guest Win10 is shut down, powered off, restart, or even shut down with machine state saved, the yellow mark in win10 system try will come back, if the ISP-5 is not connected. And, the DNS server remains 10.0.2.3 all the time!