Effects of virtualization and cloud computing on data center networks

2
Introduction
Most data centers today have a three- or four-tier hierarchical networking structure. It consists of
access layer switches, aggregation switches, and core switches (Figure 1). Three-tier networking
architectures were designed around client-server applications and single-purpose application servers.
Client-server applications caused traffic to flow primarily in North/South (N/S) patterns: from a server
up to the data center core, to the campus core where it moves out to the campus-wide network or
internet. These large core switches usually contain the vast majority of the intelligence in the network.
Figure 1: A typical data center structure today uses three layers: access, aggregation, and core.
The dotted line around the Blade server/Top of rack (ToR) switch indicates an optional layer, depending on
whether the interconnect modules replace the ToR or add a tier.
This network architecture, however, is becoming problematic for the data center. Today’s application
environments are more distributed, often with multiple tiers, and oriented toward service delivery.
These application architecture changes have resulted in:
• Greater traffic volume on the Ethernet network, including storage traffic such as FCoE and iSCSI
• More storage traffic as applications use distributed file systems and increase the amount of
synchronization and replication data across the network
• Greater traffic flow between peer servers such as server-to-server or virtual machine-to-virtual
machine—that is, East/West (E/W) rather than primarily N/S traffic flows.