Virtual Switches Demand Rethinking Connectivity for Servers
Yesterday’s Data Center: Physical Edge Switches
In a traditional data center where virtualization is not used,
each server is connected to a top-of-rack switch, typically with
two GbE connections. These network connections can provide
redundancy for fault tolerance, or they can be aggregated to
provide a total of 2 Gb bandwidth to the server. In many cases,
to provide greater redundancy, the two connections lead to
separate switches.
The top-of-rack switches, in turn, are uplinked to one or more
core switches:
•Multiple servers per connection. Trunk connections from the
top of rack switches each carry traffic between multiple servers
in the rack and the core switch infrastructure.
•High bandwidth demands. In a typical implementation, switch-
to-switch connections are based on 10 Gigabit Ethernet (10GbE).
This familiar topology is an effective means of centrally
connecting a potentially large number of servers to a core switch
infrastructure. As the environment grows, however, the large
numberofserveradaptersandswitchescancarrysignicant
capital and operating expense.
Virtualized Data Centers: Virtual Edge Switches
within Servers
Using server virtualization, the number of physical host servers
required can be reduced. Multiple VMs, each representing what
used to be a distinct physical server, can be placed on a single
host server and started and stopped independently, and they can
even use different operating systems. They can be provisioned
and brought online quickly and can be load balanced in an
automated fashion if desired. They also provide a high degree
of fault tolerance. As a result, IT can realize significant cost and
TCO savings by embracing virtualization.
Since the VMs running on a single physical host server need to
talk to each other or other systems outside of the host server,
the hypervisor must also provide network switch functionality.
That switching is analogous to the top-of-rack switches in the
non-virtualized data center.
•Each host server contains multiple virtualized servers. Now a
single physical host server represents a traditional rack of servers.
Trunked Switch-to-Switch Uplinks
Multiple Server-to-Switch
Access Connections
Figure 2. Non-virtualized servers are connected to top-of-rack switches, which are connected to core switches using large trunked uplinks.
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Virtual Switches Demand Rethinking Connectivity for Servers