Virtual Switches Demand Rethinking Connectivity for Servers

•Server adapters handle trunked traffic. Each physical
network connection is now an uplink from a host server’s virtual
switch to a physical switch, handling traffic from multiple VMs
to the outside systems. Network and Ethernet-based storage
traffic are separated and isolated from each other through the
use of VLANs. The uplinks then trunk all the different VLANs on
a single physical connection, which allows all authorized traffic
to move between the virtual switch and the physical switch.
The reduced number of physical connections (uplinks) under
this virtualized model requires fewer server adapters and
switch ports than in the non-virtualized case, helping to save
on both capital and operating expenses. The high bandwidth
requirementsforeachconnectionbenetdramaticallyfrom
using 10GbE server adapters, rather than using multiple
GbE connections.
Supporting the New Paradigm: Implications
for Networking
Today’s mainstream data center servers based on multicore
Intel® Xeon® processors provide very high levels of computing
capacity. That performance headroom
enables increasingly large numbers of VMs
per physical host. As that number grows,
providing two GbE server adapters for each
VM quickly becomes untenable.
Upgrade to 10 Gigabit Ethernet
Rather than using unwieldy numbers of GbE connections, the
virtualizedmodelclearlybenetsfromasmallernumberof
10GbE connections. Consolidating onto 10GbE trunks can also
provide better bandwidth utilization and help reduce cabling
requirements and electrical costs. Networking in the virtualized
environment follows logically from that in the non-virtualized
case, while also providing additional functionality:
•VLAN traffic segmentation. Data streams can be differentiated
logically using the switch’s VLAN functionality. As a very secure,
proven technology, VLANs provide isolation capabilities that are
comparable to those of separate physical links.
•Quality of service. The virtual switches built into leading
hypervisors provide increasingly sophisticated quality-of-
service functionality, helping to ensure that specific amounts of
bandwidth are available for various types of traffic, effectively
prioritizing it as needed.
APP
OS
VM
APP
OS
VM
APP
OS
VM
Hypervisor
Virtualized Server Rack
Software Virtual Switch
Virtual NICs
Physical
Host server
Physical
Host server
Virtual NICsVirtual NICs
Switch-to-Switch Uplinks
Figure 3. Virtualized servers are connected to switches with trunked
uplinks equivalent to non-virtualized switch-to-switch connections.
3
Virtual Switches Demand Rethinking Connectivity for Servers
3