Vultr introduced support for multiple private networks in early 2018. This feature is offered as an enhancement to the standard private networking. When enabled, you can allocate multiple isolated private networks in any of Vultr's datacenters.
Please note the following when using private networking:
Without this feature enabled, all of your compute instances in one datacenter that have private networking enabled can access your isolated private network. With multiple private networking, you can now specify which groups of instances can access specific networks, allowing you to create multiple isolated private networks. At the same time, your compute instances can attach many instances to a private network in a single location.
The "networks" section of your customer portal allows you to create one or more unique private networks. In this section, you can add one or more private networks for a specific location. A default IP range will be provided, you can use it or choose your own. To prevent issues, you should stick to the RFC1918 private address space: 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16.
To mount a private network on your compute instances, navigate to the "Settings" -> "IPv4" section of the customer portal for the specific server. In this section, you will see the "Private Network" section. Choose your network from the dropdown and click "Attach Network". Your server will be rebooted upon attaching the network. When the server finishes rebooting, an additional network interface (NIC) will be detected by the OS.
The next step is to configure the NIC at the OS level. The "Configuring Private Network" guide provides examples for the different operating systems offered by Vultr. When following the instructions on that tutorial, I recommend using an IP address from the range you have defined earlier when creating your private network. This will help you keep your network numbering organized. Vultr does not enforce specific IP address ranges on private networks, therefore it is your responsibility to properly number your networks.
If you need to add another private network, in the same location or another, the instructions here can be reused. The setup procedure is the same for additional networks.