Practical Cloud Knowledge: Install, Configure, and Manage - Deploying and Managing a Cloud Infrastructure - page 201

experts in subfields other than networking. The virtual in both virtual local area networks
and virtual networks means artificial and intangible, but when taken as a whole, the terms
stand for different things, though both are concerned with networking. Virtual networks are
essentially the software counterparts of physical networks, but the virtual local area network
is only the virtual interpretation of a LAN to an extent. It is a way to further segregate or
divide a network or multiple networks into subgroups that in many ways act as an actual
local area network and communicate as if they were attached to the same network node.
The virtual or logical counterpart of an actual local area network would still be a virtual
network, though VLANS are referred to as such because they are meant to act in many ways
similar to a local area network. More about VLANs in the next section.
Since virtual switches are not entirely different from physical switches, it would stand
that configuring them for VLANs would be the same exact thing. That's not exactly true,
though; virtual switches are only secondary to physical switches and should be configured
based on the physical switch configuration.
Interface Configuration
The VLAN interface is a logical interface that is associated with an existing VLAN and
defined at the switch. The interface can route traffic and serve as a hop junction for routing
protocols, so it has its own IP address, which is at the same subnet as that of the VLAN it
is associated with. It is not a port on the switch but exists in software, hence logical. The
interface provides the Layer 3 processing for all packets coming from all the switch ports
that are associated with the specific VLAN and also serves as the routing mechanism toward
other Layer 3 interfaces, eliminating the need for a physical router. This is also known as the
switched virtual interface (SVI) or the management interface.
To create the interface, log on to your virtualization manager's network configuration
menu or command line and input the commands. The configuration process differs depend-
ing on the software and operating system used, so consult your data sheets. You can input
the name of the VLAN as well as the associated IP address of the interface. Remember that
it has to be in the same subnet or the virtual machines connected to it will not be able to
reach it.
Configuring Virtual Machines for Several VLANs
When configuring a virtual switch for internal VLANs within the virtual environment,
all the settings can be done with the virtual switch and virtual machines without regard
for external physical switches because you will not be connecting them to external inter-
faces anyway. But if you are to configure virtual machines as part of several VLANs,
there are two easy ways to do this.
Simple Single VLAN
The first way is with a simple virtual network scenario. Say you have some virtual machines
in a network connected to a virtual switch that you need to connect to a VLAN that includes
physical machines and an external network. In this case, you can use a single physical NIC on