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17.8. Examples of Common Scenarios

This section demonstrates different virtual networking modes and provides some example scenarios.

17.8.1. Bridged Mode

Bridged mode operates on Layer 2 of the OSI model. When used, all of the guest virtual machines will appear on the same subnet as the host physical machine. The most common use cases for bridged mode include:
  • Deploying guest virtual machines in an existing network alongside host physical machines making the difference between virtual and physical machines transparent to the end user.
  • Deploying guest virtual machines without making any changes to existing physical network configuration settings.
  • Deploying guest virtual machines which must be easily accessible to an existing physical network. Placing guest virtual machines on a physical network where they must access services within an existing broadcast domain, such as DHCP.
  • Connecting guest virtual machines to an exsting network where VLANs are used.

17.8.2. Routed Mode

DMZ

Consider a network where one or more nodes are placed in a controlled sub-network for security reasons. The deployment of a special sub-network such as this is a common practice, and the sub-network is known as a DMZ. See the following diagram for more details on this layout:

Sample DMZ configuration

Figure 17.8. Sample DMZ configuration

Host physical machines in a DMZ typically provide services to WAN (external) host physical machines as well as LAN (internal) host physical machines. As this requires them to be accessible from multiple locations, and considering that these locations are controlled and operated in different ways based on their security and trust level, routed mode is the best configuration for this environment.
Virtual Server Hosting

Consider a virtual server hosting company that has several host physical machines, each with two physical network connections. One interface is used for management and accounting, the other is for the virtual machines to connect through. Each guest has its own public IP address, but the host physical machines use private IP address as management of the guests can only be performed by internal administrators. See the following diagram to understand this scenario:

Virtual server hosting sample configuration

Figure 17.9. Virtual server hosting sample configuration

17.8.3. NAT Mode

NAT (Network Address Translation) mode is the default mode. It can be used for testing when there is no need for direct network visibility.

17.8.4. Isolated Mode

Isolated mode allows virtual machines to communicate with each other only. They are unable to interact with the physical network.