Layer 7 load balancing devices, also known as Web or application switches, can drill down into URLs or HTTP headers to direct requests. An emerging technology, deep packet inspection, allows these switches to gain an even better view of content.

Web switches act as proxies for Web applications and servers sitting behind them. Users can virtualize an unlimited number of back-end Web applications and servers, providing better availability, scaling and performance. If an application or switch goes down, the switch directs client sessions to fail over to other available applications and servers without interrupting the client.

Non-HTTP-based applications or transactions would benefit from the same horizontal-scaling model. Many applications never use HTTP, and others might use HTTP only as the transport, such as Web services. Traditional Web or application switches can't do the job because HTTP is the only type of traffic they can act upon.

To extend the benefits of horizontal scaling to all IP applications, the load-balancing device needs to inspect deeper than the URL or HTTP header and into the IP datagram. Now companies can use the same architecture for non-HTTP back-office applications to provide the same economies of scale and operational efficiencies that traditional load-balancing devices have provided.

Deep packet inspection addresses this problem. This technology directs, persists, filters and logs IP-based applications and Web services traffic based on content encapsulated in a packet's header or payload, regardless of the protocol or application type. With deep packet inspection in place through a single intelligent network device, companies can boost performance without buying expensive servers or additional security products.

Complete view

Deep packet inspection lets the application traffic management device delve into the content of a TCP or User Datagram Protocol (UDP) flow for a complete view. This is accomplished by reassembling IP datagrams, TCP datastreams and UDP packets as they flow through the device to view the entire application content and then act on it according to a company's defined policies.

Through standard TCP/IP networking, messages are broken down into small packets so they can quickly traverse the network. The application traffic management device or load balancer intercepts the data on its way to the final destination, reassembles it into its original sequence and buffers it into memory.