Enable both NAT and Host Only on Ubuntu 18.04

Question

I am using Ubuntu 18 minimal image to create an Ubuntu server with VirtualBox. I created a host only network and added adapter to vm along with NAT adapter (already configured).

The original configuration of netplan was the following:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      dhcp4: yes

I changed this configuration to the following to enable host only adapter (enp0s8):

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      dhcp4: ye
    enp0s8:
      dhcp4: no
      addresses: [192.168.56.101/24]
      gateway4: 192.168.56.1

Now I am successfully able to access the VM from the host machine over the network. But internet inside the VM stops working :(. I have tried so many different solutions but either I get internet working (provided by NAT adapter) by disabling host only adapter, or can access vm from host by enabling host only adapter.

I suspect the VM is trying to connect to internet via host only adapter. How can I change this?

Answer 1

I am also hitting the same issue. I am able to get it work by removing this line:

      gateway4: 192.168.56.1

There are other alternatives discussed in netplan configuration on Ubuntu 17.04 virtual machine, however what I need is just to set up a lab environment for testing, so I didn't try those out.

Answer 2

I have almost very similar situations, but not exactly the same. I want to share the problem and solution for my setup here, because the final step that make it works was the answer stated by @victor6510 above.

I have Ubuntu Server (18.0.4) guest running inside LinuxMint host. I have setup the server initially as follow:

• Network: Bridged-Adapter (fixed IP on my home router's network)

I have a VPN client in the LinuxMint host. My objective is to allow the Ubuntu guest to access server through the VPN connection. It was not easy, but after some reading, I decided the NAT adapter option is the most likely solution. Hence I did the following:

1. Add new network adapter in VirtualBox settings for my Ubuntu guest (NAT)
2. Reboot Ubuntu guest
3. Configure netplan setting for the Ubuntu guest
4. Do netplan generate & netplan apply

Here is my netplan configuration inside the Ubuntu guest:

network:
  ethernets:
    enp0s3:
        dhcp4: no
        addresses: [192.168.1.200/24]
        #gateway4: 192.168.1.254
        nameservers:
                addresses: [8.8.8.8,8.8.4.4]
    enp0s8:
        dhcp4: yes
  version: 2

enp0s3 is the Bridged adapter

enp0s8 is the NAT adapter

Before I commented the line gateway4: 192.168.1.254, Internet and ping stopped from working. Once commented, I have Internet, and able to connect to my server on the other side of the VPN. Hope this will help anyone facing similar situation.

NOTE: I don't know details setting of the VPN server I connected to.

Answer 3

In short when we have both NAT and host-only adapter for a VM.Then make sure for host-only adapter we do not have gateway4 defined.

For example in yaml file

network:
 ethernets:
   enps08:
     addresses: [192.168.56.100/24]
     dhcp: no
     #gateway4: 192.168.56.1
version 2 

The above configuration works.