To add an additional network interface to an instance or to remove an interface from your instance perform the steps described below.

Please note: The steps below only provide a basic overview. The exact tasks required will vary depending on your network design. Please refer to the GCP documentation for details.

1 General Information
2 Create VPCs and Subnets for Instance
3 Adding Additional NICs to an Instance
4 Assigning a Static IP Address to a Network Interface
5 Detaching a Network Interface from an Instance
6 Address Assignment Information
- 6.1 General information
- 6.2 Address Ranges
7 Interface Configuration on Linux
8 Additional GCP-specific Information
- 8.1 IP Interface Netmask
- 8.2 Routing between VPCs
- 8.3 Network Interface MTU

When an instance is created, a default Ethernet interface is attached to the system. This default network interface is mandatory. During the creation of the instance, you can add additional network interfaces.

General Information

The rules for Google cloud instances with respect to network interfaces are strict:

Interfaces can only be added during instance creation.
Each network interface configured in a single instance must be attached to a different VPC network.
The additional VPC networks that the multiple interfaces will attach to must exist before an instance is created. See Using VPC Networks for instructions on creating additional VPC networks.
You cannot delete a network interface without deleting the instance.

Therefore the required VPCs and subnets must exist before the instance is created.

To create additional VPCs (if required), perform the steps below.

Create VPCs and Subnets for Instance

Step 1: Open the VPC network section by clicking on the Navigation menu, then selecting VPC network, and clicking on VPC networks - as illustrated below.

This will open the VPC overview page with the already existing VPCs. If all required VPCs and subnets already exist, continue with creating the new VM instance. Otherwise, continue with step 2.

Step 2: If you need to create a new VPC, click on CREATE VPC NETWORK at the top of the VPC overview list.

This opens the VPC configuration window.

Step 3: Create VPC and subnets.

In the VPC configuration window, enter

the VPC name, and
the subnet name, region and address.

Click on Create at the bottom of the window to create the VPC.

The new VPC should appear in the VPC overview list. Selecting the VPC in the overview list will open the detail information window. Example:

Step 4: Create firewall rules for the VPC.

With the detail information open, click on Firewall. This will allow you to define the required firewall rules for the VPC.

An example of a small set of firewall rules that allow incoming SSH and ICMP is shown below:

Adding Additional NICs to an Instance

Additional NICs are added during instance creation. Perform the following steps in the instance creation window:

Open the advanced settings at the bottom of the VM creation window by clicking on Management, security, disks,... at the bottom of the page.
Select Networking from the advanced settings section.
Click on Add network interface.
Select the correct subnet (created before).
Set the information about internal and external IP address (static or ephemeral) as required.

After adding all the required information, click on Done.

The second interface is now visible in the details page of the VM instance:

Assigning a Static IP Address to a Network Interface

During the creation of a VM instance, when you add the default and optional additional NICs, you can determine if the IP addresses assigned to a NIC are static (persistent across restarts) or ephemeral (non-persistent across restarts). The process to add a static IP requires reserving the IP address. The public IP address may also have to be created first.

If you choose to add a static private IP address to an interface, you will get the following window to reserve a static private IP address:

If you choose to add a static public IP address to an interface, you will get the following window to create (if needed) and reserve an address:

You can also manage external IP addresses from the VPC network management section (Navigation menu > VPC network > External IP addresses):

Detaching a Network Interface from an Instance

You cannot delete a network interface without deleting the instance it is attached to. So if you do not need a network anymore, but do not want to delete the instance, you can only disable it from the operating system level.

Address Assignment Information