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Ubuntu: Unable to get IP for network interface / Using multiple network adapters

This is a very focused article on a similar issue which i encountered very recently.

Problem: I recently installed Ubuntu Server 20.0 on a virtualBox. My intention was to use 2 network adapters as shown in the picture below.
  1. Host-Only Network
  2. NAT
After setting up, I realised that i could not get IP address for the NAT adapter and it was always DOWN.

Solution: Ubuntu20.0 comes with a different Newtork Configuration System compared to older ones like Ubuntu 14. The new Ubuntu uses netplan to handle network configurations.
To solve this issue, you need to add specific information about every adapter into the netplan configuration file. The first adapter will always be configured by default.

Follow through this article to learn how in 5 easy steps.

1. The picture below shows that my VM is already configured to use 2 network adapters.




2. Now i powered up the VM and check my network parameters.
I powered the VM and ran the commands to check if my 2 network adapters were functional.

ip addr


Here's the result below:
This impllies that my Host-Only Network(enp0s3) is fine and running at 192.168.56.101.
But this also shows that my second network adapter interface is down. Dont try running a command to bring it up because it will still not be functional and it will go down again after reboot.

3. Remember I mentioned Netplan. The netplan config file is any 
.yaml
file in the netplan directory.
Netplan Directory: 
/etc/netplan/

from the previous step, observe that 
enp0s3
refers to my Host-Only Network interfcae, while 
enp0s8
refers to my NAT interface. Lets open the netplan config files to see the default configuration.

As you can see, only my HostOnlyNetwork is configured, I need to add an additional entry for my new interface.

4. Be careful when handling yaml files, they have strict indentation pattern, and any little mistake means the configuration file will not be useful to the System.
You must be the root user before you can edit the netplan configuration yaml files.
Sample Commands:
nano /etc/netplan/00-installer-config.yaml

Copy the file contents and paste on the next line.
Change the interface name on the new entry so that it shows the name of your second adapter.
when you are done press 
Ctrl+X
to save, press 
Enter
to ensure the file name remains same.

The picture above shows that I duplicated the initial content of the file and simply changed the interface name for enp0s8 before saving the yaml file.

5. Now Reboot your Virtual machine.

6. Now run the command to show your network interfaces again.
ip addr

As you can see, the NAT Adapter interface is now showing and it also has an IP address. the NAT adapter will allow this VM talk to the internet and also other VM on the same virtualBox.
The HostOnly Network will ensure the the Host computer can ssh into the VM at anytime.

Thats all. At present I am not sure why only the first interface is configured by default but it was nice to see this solved. I hope this article helps you. Feel free to reach out to me. Love you and thanks for reading. We can also set the DHCP4 to false. Detils will be provided in a future article.
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