Layer 7 Switching Routes Data Discerningly

Burgeoning Internet traffic coupled with rising demand for QOS multimedia content such as VOIP and real-time streaming have fueled the emergence of Layer 7 switching.

Layer 7 switching is a multifaceted technology that involves not only the switches, but also the design and architecture of the network where the switches operate. It is a complex, high-end proposition that is best suited to organizations with a large-scale Web presence. Although smaller-scale Web operations can also benefit from limited deployments of Layer 7 switching, its greatest potential is in settings where quality of service is critical and where networks are designed with this technology in mind.

eWeek Labs advises IT managers to understand their needs thoroughly before investing in Layer 7 switching schemes.

Layer 7 switching, also known as content-based switching, works by distinguishing data streams by specific URLs, application types and individual protocols. For example, a Layer 7 switch can examine a packets header information, identify the application type and direct the request based on detailed information that switches operating at Layer 4 cannot comprehend.

Layer 7 switching meshes well with emerging infrastructure designs that enable a large Web server farm to use a single IP address to represent multiple servers (see diagram). Through the effective use of Network Address Translation and URL switching, Layer 7 switching has facilitated the growth of virtual server farms where content is spread over multiple servers of varying capacities. An efficient Layer 7 implementation directs traffic intelligently at close-to-Ethernet wire speeds.

Application data (such as data from an HTTP request or Oracle Corp. database log-in) is buried deep in a network packet. To examine that data, a switch must look all the way to the application layer. A Layer 7 switch can examine protocol information such as H.323 or Session Initiation Protocol, which is buried within Layer 7.

For Internet service providers or large corporations dealing with real-time and delay-sensitive applications such as VOIP (voice over IP) and videoconferencing, the need for traffic prioritization based on QOS cannot be understated. A Layer 7 switch can discern between packet types with unprecedented accuracy and minimal delays and can assign priority levels to time-sensitive data.

Layer 7 switches, such as Foundry Networks Inc.s ServerIron and ArrowPoint Communications Inc.s CS-800, provide the ability to route traffic on the basis of application-specific content in network packets.

Vendors such as Foundry and Cisco Systems Inc., which acquired Layer 7 switch vendor ArrowPoint, have developed true Layer 7 switches with switch fabric, CPU, memory and switching software optimized for Layer 7 switching.

Meanwhile, many vendors sell Layer 2 and Layer 3 switches with limited Layer 7 capabilities. These switches can perform Layer 7 packet examination but are designed for switching at lower layers. As a result, URL examination takes place on a nonoptimized backplane and CPU, and heavy Layer 7 loads will bring the switch to its knees.

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