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2.4. Network

The Red Hat Enterprise Virtualization network architecture facilitates connectivity between the different elements of the Red Hat Enterprise Virtualization environment. This includes communication between the Red Hat Enterprise Virtualization Manager and hosts, communication between individual hosts, and storage communication between hosts and network attached storage. The network architecture also facilitates connectivity among virtual machines, communication between virtual machines and network attached storage, and communication between virtual machine users or clients and their virtual machines. The Red Hat Enterprise Virtualization network architecture also allows optional connectivity to destinations and objects that are external to the Red Hat Enterprise Virtualization environment.
The Red Hat Enterprise Virtualization network architecture not only supports network connectivity, it also allows for network segregation. Hosts in separate clusters can be isolated from each other, as can virtual machines hosted in separate clusters. Virtual machines used for specific purposes can connect to special purpose networks, and can be isolated from general purpose virtual machines. Network traffic can also be segregated by traffic type. Storage traffic and display traffic can be carried on separate networks, for example.
Network Architecture
Figure 2.4. Network Architecture

In order to support all these networking possibilities, networking is defined in Red Hat Enterprise Virtualization in several layers. The underlying physical networking infrastructure must be in place and configured to allow connectivity between the hardware and the logical components of the Red Hat Enterprise Virtualization environment.
Networking Infrastructure
The Red Hat Enterprise Virtualization network architecture relies on some common hardware and software devices:
  • Network Interface Controllers (NICs) are physical network interface devices that connect a host to the network.
  • Virtual NICs (VNICs) are logical NICs that operate using the host's physical NICs. They provide network connectivity to virtual machines.
  • Bonds bind multiple NICs into a single interface or bridge.
  • Bridges are a packet-forwarding technique for packet-switching networks. They form the basis of logical networks.
Logical Networks
Logical networks allow segregation of network traffic based on environment requirements. A logical network is implemented at the host level as a software bridge device. By default, one logical network is defined during the installation of the Red Hat Enterprise Virtualization Manager: the rhevm Management network. Other logical networks that can be added by an administrator are: a dedicated storage logical network, and a dedicated display logical network.
Data Center Layer
Logical networks are defined at the data center level. Each data center has a management network. Further logical networks are optional but recommended. IP address, gateway, subnet mask, and VLAN tagging can be set at the data center level, but at this level the network is purely logical. A logical network that is defined for a data center must also be added to the clusters that use the logical network.
Cluster Layer
Logical networks are made available from a data center, and must be added to the clusters that will use them. Each cluster is connected to the management network by default. You can optionally add to a cluster logical networks that have been defined for the cluster's parent data center. When a logical network has been added to a cluster, it must be implemented for each host in the cluster.
Host Layer
Logical networks are implemented for each host in a cluster as a software bridge device associated with a physical NIC. Each host has the management network implemented as a bridge using one of its network devices as a result of being included in a Red Hat Enterprise Virtualization environment. Further logical networks that have been added to a cluster must be associated with NICs on each host to become operational for the cluster.
Virtual Machine Layer
Logical networks can be made available to virtual machines in the same way that a network can be made available to a physical machine. A virtual machine can have its virtual NIC connected to any logical network that has been implemented on the host that runs it. The virtual machine then gains connectivity to any other devices or destinations that are available on the logical network it is connected to.
Example 2.1. Management Network
The management logical network, named rhevm, is created automatically when the Red Hat Enterprise Virtualization Manager is installed. The rhevm network is dedicated to management traffic between the Red Hat Enterprise Virtualization Manager and hosts. If no other specifically-purposed bridges are set up, rhevm is the default bridge for all traffic.

See Chapter 4, Network Architecture for more information on the Red Hat Enterprise Virtualization network architecture.