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Managing virtualization

Virtualization networking guide:
Managing virtualization
Virtualization is a white hot topic in the IT world, and with good
reason. It’s vital for networking professionals to understand how
server virtualization and networks affect each other. In this expert eguide
learn about managing virtualization networking, distributed
virtual switching, network capacity planning for virtualization and
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Virtualization networking guide:
Managing virtualization
Table of Contents
Virtualization networking guide: Managing virtualization
Resources from Dell and VMware E-Guide
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Virtualization has gone from IT buzzword to IT staple, so it’s vital for networking
professionals to understand how server virtualization and networks affect each other. In a
server virtualization environment, every host server abstracts and extends the network into
its hypervisor, where a virtual switch manages traffic between virtual machines. Server
virtualization also introduces I/O bottlenecks and bandwidth capacity problems on the
physical network by increasing the amount of traffic generated by individual physical
servers. Consequently, virtualization networking — or networking for virtualization — is on
every networking professional’s agenda.
In this guide, networking professionals can learn about managing virtualization networking,
distributed virtual switching, network capacity planning for virtualization and more.
Considerations for virtual server networking
Server virtualization networking requires involvement from the networking team at several
key points — including network capacity planning, configuration mapping and management,
and network automation — to support fluid virtual machines and changing traffic patterns.
Check out the resources below in each category to find out more about network
considerations for virtualization.
Planning for virtualization networking
In planning for virtualization, network managers must remember that demand for power
and network capacity changes depending on peak traffic hours. For example, when the
number of physical servers is reduced, the number of users on each server increases
proportionately. Power usage and network utilization for those servers must be monitored
and managed accordingly, and network managers must be ready to turn bandwidth up and
down depending on need. E-Guide
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Virtualization and network configuration
While virtualization can save companies quite a bit of money by reducing the number of
physical servers in the data center, it can also cause headaches for network managers
trying to map and manage ever-changing network configuration. Virtual machine (VM)
sprawl can also cause security problems since it is difficult to set a security configuration
that will follow a moving virtualized application. Many IT organizations solve this by setting
up clusters of physical servers for similar applications that require comparable security and
network settings. But as application demand grows, these clusters will run out of capacity,
requiring manual network reconfigurations.
Network automation software can solve this problem by automatically allocating the
necessary bandwidth and power while provisioning VMs to handle workloads on demand.
Server virtualization also impacts the network by creating constantly changing and
multiplying media access control (MAC) addresses. MAC addresses are generally burned into
the network interface cards (NICs) on the servers and are a fixed value in a nonvirtualization
environment. But in a virtualized environment, a MAC address can change
during “cold migration” — when a VM is shut down and moved from one location to another.
Any configurations built around the old MAC address will no longer apply to the new
address. While this isn’t a prolific problem (as there aren’t many instances in which network
admins configure things based on the MAC address), it is a problem where these
configurations do exist.
The human factor in virtualization networking
One of the biggest challenges the IT team faces with virtualization is the requirement for
more collaboration between the network team and the server team. The implementation of
VLANs is the perfect example of the need for teamwork. VLANs are crucial in managing
network traffic flow in a virtual environment, but they are tightly integrated into server
management as well. VLAN configuration occurs on switches and on physical servers
running the server virtualization software. E-Guide
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Network admins and server admins will also need to share information about which NICs are
plugged into which network ports for link aggregation purposes, which allows the
virtualization solution to provide redundancy and/or more efficient use of multiple physical
Virtualization and network performance
Server virtualization can seriously affect network performance. The consolidation of
workloads onto fewer physical servers can affect traffic flow within the network, disrupting
network performance and throughput. In a non-virtualized environment, fixed-configuration
switches, or “rack switches,” provide uplinks to the core network, and traffic aggregation
occurs within the rack switch itself. But when server virtualization is implemented, traffic
aggregation occurs at the physical server level, not on the rack switch. Server workload
consolidation leads to heavier use of the network links to the physical servers. Using a rack
switch to uplink to the core to try to aggregate already aggregated traffic can result in
bottlenecks and thus major problems in network performance and throughput.
Site consolidation can also affect network latency. With enterprises consolidating multiple
data centers and pulling out branch office data systems, the entire wide area network
(WAN) can be affected. Let’s take this analogy from Harold Byun, senior product marketing
manager at Riverbed: 200 passengers need to drive from New York to Los Angeles. A small
car that can carry only five passengers at a time would need to make 40 roundtrips to get
everyone to LA. Building a new freeway with wider lanes and better traffic flow won’t help —
the car still has to make 40 trips, no matter how you cut it. With great distance over a WAN,
a network will experience latency, regardless of how upgraded the network link is. The
solution is to minimize the number of “trips” that applications must make across the
network. By encapsulating the overhead of standard office application protocols, which are
running over a wider network in a more consolidated virtual environment, the network can
make fewer trips to carry data. With this analogy, large buses that can carry 50 passengers
would be replacing the cars, reducing the number of trips from 40 to four.
Another solution would be WAN acceleration. This can be achieved with WAN optimization
controllers (WOCs), which are a type of virtual appliance based on network appliance E-Guide
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software running on a VM. Other virtual appliances include application delivery controllers
(ADCs), and virtual appliances work in conjunction with virtual desktops and virtual servers.
Virtualization networking was once a game of hit or miss for network managers, but the
emergence of third-party virtual switches and distributed virtual switching strategies has
given the networking team more control over the environment. In this section, learn about
distributed virtual switch implementation and managing virtual servers through networking.
Managing virtualization through the network
Virtual switching: Managing virtualization through the network
A virtual switch is software that emulates a physical Ethernet switch and allows one VM to
communicate with another. The switch inspects packets before passing them on and is often
included as part of virtualization software or in a server’s hardware as part of its firmware.
Because of this, the server management team usually claims responsibility for management
of virtual switches. But proposed changes to virtual switch standards, including the Virtual
Ethernet Port Aggregation (VEPA) and the VN-Tagging port extension approach, give the
networking team more control over the virtual switching that takes place in server
virtualization. How the proposed changes will affect the relationship between the server and
network teams is anyone’s guess, but data center managers and CIOs need to keep the
possible disharmony in mind.
As previously mentioned, a major challenge with virtualization is figuring out how to move
VMs across physical hosts without continuously having to reconfigure them individually.
Virtual switching can address this challenge.
Technologies like VMware’s vSwitch and vSphere can make this happen by combining the
resources of multiple physical hosts. Among vSphere’s networking features are distributed
vSwitches, which allow a single switch to be used across multiple hosts; private VLANs,
which let administrators control and restrict communication between VMs on a vSwitch; and
IPv6 support, which allows for the 16-byte, hexadecimal IPv6 addresses that will become
more widely used once the industry starts to experience exhaustion of IP addresses E-Guide
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supported by IPv4. But these technologies can cause a bottleneck. Administrators can
address this by using virtual switches in conjunction with virtual appliances, such as the
Arista virtual Extensible Operating System (vEOS), which can make the vSwitch more
scalable for network administrators.
Managing virtual switches is no easy feat. There are several virtual switch problems,
including limited traffic visibility, poor manageability, and inconsistent network policy
enforcement, as well as limited I/O bandwidth. (Read more about virtual switch challenges.)
But some solutions to these virtual network switch woes exist, including edge virtualization
technologies such as distributed virtual switching (DVS), edge virtual bridging (EVB) and
single root I/O virtualization (SR-IOV).
DVS is the aggregation of multiple virtual switches. It simplifies a network engineer’s task
by allowing him to configure servers in clusters across the network instead of configuring
each one individually. The control plane and the data plane of the virtual switch are decoupled,
allowing the data planes of multiple virtual switches to be controlled by an external
centralized management system. This de-coupling allows the vSwitch control plane to be
tightly integrated with the control planes of physical access switches and/or the virtual
server management system. With DVS, the shortcomings of traditional vSwitches can be
The Cisco Nexus 1000v distributed virtual switch is an option for addressing vSwitch
shortcomings. It works with any manufacturer’s physical switch, so non-Cisco physical
networks can use the 1000v for virtual network management.
802.1Q VLAN tagging
Configuring vSphere VLANs is as challenging and complex as establishing VLANs in a typical
physical network. 802.1Q VLAN tagging is a popular method for tackling the problem of
configuring vSphere VLANs. The 802.1Q networking standard allows multiple bridged
networks to transparently share the same physical network link without leaking of
information among the networks. 802.1Q VLAN tagging allows for multiple VLANs to be used
on a single physical switch port, enabling a network administrator to reduce the number of
physical NICs on a server from one per VLAN to one per host. E-Guide
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Tagging applies tags to all network frames to identify them as belonging to a particular
VLAN. The types of VLAN tagging include virtual machine guest tagging (VGT mode),
external switch tagging (EST mode), and virtual switch tagging (VST mode). VST mode is
the most commonly used with VLANs in vSphere because it’s the easiest to configure and
manage, and it also eliminates the need to install a specific VLAN driver inside a virtual
Network management in a virtualized environment
It’s not easy to manage virtual network relationships. In the “old days,” infrastructure was
static. Applications lived on dedicated physical servers with static NICs that could be
configured once and forgotten. But finding a way to “reconnect” physical resources and
virtual workloads that are mobile and fluid is a challenge. Many vendors are developing
products that offer an “end-to-end” view of physical resources and how they are being
utilized by virtual workloads at any given time. In the meantime, there are various steps
toward managing virtual network relationships that an IT organization can take, including
documentation, live migration limitation, and management tools.
Another important tool in virtualization network management is network change and
configuration management (NCCM), which is significantly more challenging in a virtualized
environment. Use this primer on virtualization change and configuration management to
further your understanding of this concept. E-Guide
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Resources from Dell and VMware
The Power of Virtualization: A Management Series for SMB, Part 1 – Virtualization
Networking Best Practices for VMware® Infrastructure 3 on Dell™ PowerEdge™
The Benefits of SMB Virtualization using Dell and VMware – IT Efficiency for
Organizations of all Sizes
About Dell and VMware
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