Providing a dedicated NIC for guest operating systems is the standard method in non-cloud environments. However, this configuration poses some challenges in cloud environments where MAC address / IP address combinations are fixed parameters set by the cloud provider.

This section will provide some information about how to configure such a setup in a cloud environment.

Basic Concept

The following images illustrates the basic concept when working with a dedicated network interface for the guest operating system. There are, of course, many variations depending on the specific environment.

Scenario: host and guest system have a dedicated NIC. The NIC used by the Charon host has a private and a public IP address, the NIC used by the guest system a private IP address and optionally a public IP address.

If the NIC dedicated to the guest OS does not have a public IP address, the guest system may still be able to access the Internet via the customer network reachable across a VPN gateway. This will depend on the customer specific network configuration. This type of connection is the recommended way to provided external network access to the guest system as the VPN ensures that traffic across a public network is encrypted.

The basic steps to implement the above configuration are as follows:

• Create a cloud instance in which the Charon host system runs.
• Add two NICs to the Charon host system. One for the Charon host and one for the guest system.
• Configure the appropriate access rules for instance and NICs.
• One NIC is dedicated to the Charon host, one to the guest system. Configure a private and public IP address for the NIC used by the Charon host. Configure a private IP address for the NIC used by the guest system (and optionally a public IP address - not recommended).
• On the Charon host, remove the private IP address from the NIC dedicated to the guest system if it was automatically configured and ensure that the interface will be enabled when the system starts.
• Assign the appropriate NIC to the guest system.
• Configure the guest system MAC address to be the same as the the one of the NIC selected for the guest.
• After booting the guest system, configure the private IP originally assigned to the guest NIC by the cloud provider as the IP address of the guest Ethernet interface.
• Set the default route of the guest system to the default gateway or VPN gateway of the LAN.

Depending on firewall rules and cloud-specific security settings, the guest system should then be able

• to communicate with the host system,
• other systems in cloud-internal network (e.g. other guest and host systems), 
• the customer internal network via a previously configured VPN gateway,
• directly with the Internet if a public IP address was configured for the interface (not recommended).

Additional sections in this manual show the basic configuration steps for the above examples.

 In this scenario any traffic between host and guest system (if configured with a public IP address) and external systems reachable via the Internet gateway is not encrypted by default. If this traffic runs across a public network, it is exposed to being monitored and even modified by third parties. The user is responsible for ensuring data protection conforming to the user's internal security rules. It is strongly recommended to use encrypted VPN connections for any sensitive traffic.

 Guest operating systems are often old and no longer maintained by the original vendor. This means they are more easily compromised by attacks from the Internet. Therefore, direct Internet access for the guest system is not recommended.

The actual configuration steps vary depending on the cloud environment used. Some examples are provided in further sections of this document.